При нажатии на любую кнопку ничего не происходит

Я кое-что исправил и написал вам в коде, но вам еще надо много трудиться. Удачи вам.

from decimal import *
from math import *
from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_Calculator(object):
    def setupUi(self, Calculator):
        Calculator.setObjectName("Calculator")
        Calculator.resize(322, 386)
        Calculator.setStyleSheet("background-color: rgb(0, 0, 0);")
        self.centralwidget = QtWidgets.QWidget(Calculator)
        self.centralwidget.setObjectName("centralwidget")
        self.display = QtWidgets.QLabel(self.centralwidget)
        self.display.setGeometry(QtCore.QRect(-1, 0, 322, 61))
        self.display.setStyleSheet("font: 25pt \"Nirmala UI\";\n"
"color: rgb(255, 255, 255);")
        self.display.setAlignment(QtCore.Qt.AlignRight|QtCore.Qt.AlignTrailing|QtCore.Qt.AlignVCenter)
        self.display.setObjectName("display")
        self.btn_c = QtWidgets.QPushButton(self.centralwidget)
        self.btn_c.setGeometry(QtCore.QRect(0, 126, 65, 65))
        self.btn_c.setStyleSheet("font: 18pt \"Nirmala UI\";\n"
"color: rgb(255, 109, 25);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_c.setObjectName("btn_c")
        self.btn_dot = QtWidgets.QPushButton(self.centralwidget)
        self.btn_dot.setGeometry(QtCore.QRect(194, 64, 65, 65))
        self.btn_dot.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 109, 25);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_dot.setObjectName("btn_dot")
        self.btn_proc = QtWidgets.QPushButton(self.centralwidget)
        self.btn_proc.setGeometry(QtCore.QRect(65, 322, 65, 65))
        self.btn_proc.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 255, 255);\n"
"background-color: rgb(255, 109, 25);")
        self.btn_proc.setObjectName("btn_proc")
        self.btn_div = QtWidgets.QPushButton(self.centralwidget)
        self.btn_div.setGeometry(QtCore.QRect(258, 64, 65, 65))
        self.btn_div.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 109, 25);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_div.setObjectName("btn_div")
        self.btn_7 = QtWidgets.QPushButton(self.centralwidget)
        self.btn_7.setGeometry(QtCore.QRect(66, 128, 65, 65))
        self.btn_7.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 255, 255);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_7.setObjectName("btn_7")
        self.btn_8 = QtWidgets.QPushButton(self.centralwidget)
        self.btn_8.setGeometry(QtCore.QRect(130, 128, 65, 65))
        self.btn_8.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 255, 255);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_8.setObjectName("btn_8")
        self.btn_9 = QtWidgets.QPushButton(self.centralwidget)
        self.btn_9.setGeometry(QtCore.QRect(194, 128, 65, 65))
        self.btn_9.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 255, 255);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_9.setObjectName("btn_9")
        self.btn_mult = QtWidgets.QPushButton(self.centralwidget)
        self.btn_mult.setGeometry(QtCore.QRect(258, 128, 65, 65))
        self.btn_mult.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 109, 25);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_mult.setObjectName("btn_mult")
        self.btn_4 = QtWidgets.QPushButton(self.centralwidget)
        self.btn_4.setGeometry(QtCore.QRect(66, 192, 65, 65))
        self.btn_4.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 255, 255);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_4.setObjectName("btn_4")
        self.btn_plus = QtWidgets.QPushButton(self.centralwidget)
        self.btn_plus.setGeometry(QtCore.QRect(258, 256, 65, 65))
        self.btn_plus.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 109, 25);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_plus.setObjectName("btn_plus")
        self.btn_5 = QtWidgets.QPushButton(self.centralwidget)
        self.btn_5.setGeometry(QtCore.QRect(130, 192, 65, 65))
        self.btn_5.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 255, 255);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_5.setObjectName("btn_5")
        self.btn_6 = QtWidgets.QPushButton(self.centralwidget)
        self.btn_6.setGeometry(QtCore.QRect(194, 192, 65, 65))
        self.btn_6.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 255, 255);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_6.setObjectName("btn_6")
        self.btn_1 = QtWidgets.QPushButton(self.centralwidget)
        self.btn_1.setGeometry(QtCore.QRect(66, 256, 65, 65))
        self.btn_1.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"gridline-color: rgb(255, 255, 255);\n"
"color: rgb(255, 255, 255);")
        self.btn_1.setObjectName("btn_1")
        self.btn_3 = QtWidgets.QPushButton(self.centralwidget)
        self.btn_3.setGeometry(QtCore.QRect(194, 256, 65, 65))
        self.btn_3.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 255, 255);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_3.setObjectName("btn_3")
        self.btn_2 = QtWidgets.QPushButton(self.centralwidget)
        self.btn_2.setGeometry(QtCore.QRect(130, 256, 65, 65))
        self.btn_2.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 255, 255);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_2.setObjectName("btn_2")
        self.btn_min = QtWidgets.QPushButton(self.centralwidget)
        self.btn_min.setGeometry(QtCore.QRect(258, 192, 65, 65))
        self.btn_min.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 109, 25);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_min.setObjectName("btn_min")
        self.btn_zero = QtWidgets.QPushButton(self.centralwidget)
        self.btn_zero.setGeometry(QtCore.QRect(130, 320, 65, 65))
        self.btn_zero.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 255, 255);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_zero.setObjectName("btn_zero")
        self.btn_eq = QtWidgets.QPushButton(self.centralwidget)
        self.btn_eq.setGeometry(QtCore.QRect(258, 322, 65, 65))
        self.btn_eq.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 255, 255);\n"
"background-color: rgb(255, 109, 25);")
        self.btn_eq.setObjectName("btn_eq")
        self.btn_debug = QtWidgets.QPushButton(self.centralwidget)
        self.btn_debug.setGeometry(QtCore.QRect(193, 322, 65, 65))
        font = QtGui.QFont()
        font.setFamily("Nirmala UI")
        font.setPointSize(14)
        font.setBold(False)
        font.setItalic(False)
        font.setWeight(50)
        self.btn_debug.setFont(font)
        self.btn_debug.setStyleSheet("font:\"Nirmala UI\";\n"
"color: rgb(255, 255, 255);\n"
"background-color: rgb(255, 109, 25);")
        self.btn_debug.setObjectName("btn_debug")
        self.btn_basp = QtWidgets.QPushButton(self.centralwidget)
        self.btn_basp.setGeometry(QtCore.QRect(0, 64, 65, 65))
        self.btn_basp.setStyleSheet("font: 18pt \"Nirmala UI\";\n"
"color: rgb(255, 109, 25);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_basp.setObjectName("btn_basp")
        self.btn_pi = QtWidgets.QPushButton(self.centralwidget)
        self.btn_pi.setGeometry(QtCore.QRect(0, 322, 65, 65))
        self.btn_pi.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 255, 255);\n"
"background-color: rgb(255, 109, 25);")
        self.btn_pi.setObjectName("btn_pi")
        self.btn_deg = QtWidgets.QPushButton(self.centralwidget)
        self.btn_deg.setGeometry(QtCore.QRect(0, 257, 65, 65))
        self.btn_deg.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 255, 255);\n"
"background-color: rgb(255, 109, 25);")
        self.btn_deg.setObjectName("btn_deg")
        self.btn_rox = QtWidgets.QPushButton(self.centralwidget)
        self.btn_rox.setGeometry(QtCore.QRect(0, 192, 65, 65))
        self.btn_rox.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 255, 255);\n"
"background-color: rgb(255, 109, 25);")
        self.btn_rox.setObjectName("btn_rox")
        self.btn_bl = QtWidgets.QPushButton(self.centralwidget)
        self.btn_bl.setGeometry(QtCore.QRect(66, 64, 65, 65))
        self.btn_bl.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 109, 25);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_bl.setObjectName("btn_bl")
        self.btn_br = QtWidgets.QPushButton(self.centralwidget)
        self.btn_br.setGeometry(QtCore.QRect(130, 64, 65, 65))
        self.btn_br.setStyleSheet("font: 22pt \"Nirmala UI\";\n"
"color: rgb(255, 109, 25);\n"
"background-color: rgb(0, 0, 0);")
        self.btn_br.setObjectName("btn_br")
        self.btn_eq.raise_()
        self.display.raise_()
        self.btn_c.raise_()
        self.btn_dot.raise_()
        self.btn_proc.raise_()
        self.btn_div.raise_()
        self.btn_7.raise_()
        self.btn_8.raise_()
        self.btn_9.raise_()
        self.btn_mult.raise_()
        self.btn_4.raise_()
        self.btn_plus.raise_()
        self.btn_5.raise_()
        self.btn_6.raise_()
        self.btn_1.raise_()
        self.btn_3.raise_()
        self.btn_2.raise_()
        self.btn_min.raise_()
        self.btn_zero.raise_()
        self.btn_debug.raise_()
        self.btn_basp.raise_()
        self.btn_pi.raise_()
        self.btn_deg.raise_()
        self.btn_rox.raise_()
        self.btn_bl.raise_()
        self.btn_br.raise_()
        Calculator.setCentralWidget(self.centralwidget)

        self.retranslateUi(Calculator)
        QtCore.QMetaObject.connectSlotsByName(Calculator)

    def retranslateUi(self, Calculator):
        _translate = QtCore.QCoreApplication.translate
        Calculator.setWindowTitle(_translate("Calculator", "Calculator"))
        self.display.setText(_translate("Calculator", "0"))
        self.btn_c.setText(_translate("Calculator", "C"))
        self.btn_dot.setText(_translate("Calculator", ","))
        self.btn_proc.setText(_translate("Calculator", "%"))
        self.btn_div.setText(_translate("Calculator", "÷"))
        self.btn_7.setText(_translate("Calculator", "7"))
        self.btn_8.setText(_translate("Calculator", "8"))
        self.btn_9.setText(_translate("Calculator", "9"))
        self.btn_mult.setText(_translate("Calculator", "×"))
        self.btn_4.setText(_translate("Calculator", "4"))
        self.btn_plus.setText(_translate("Calculator", "+"))
        self.btn_5.setText(_translate("Calculator", "5"))
        self.btn_6.setText(_translate("Calculator", "6"))
        self.btn_1.setText(_translate("Calculator", "1"))
        self.btn_3.setText(_translate("Calculator", "3"))
        self.btn_2.setText(_translate("Calculator", "2"))
        self.btn_min.setText(_translate("Calculator", "−"))
        self.btn_zero.setText(_translate("Calculator", "0"))
        self.btn_eq.setText(_translate("Calculator", "="))
        self.btn_debug.setText(_translate("Calculator", "DEBUG"))
        self.btn_basp.setText(_translate("Calculator", "⌫"))
        self.btn_pi.setText(_translate("Calculator", "?"))
        self.btn_deg.setText(_translate("Calculator", "x²"))
        self.btn_rox.setText(_translate("Calculator", "√"))
        self.btn_bl.setText(_translate("Calculator", "("))
        self.btn_br.setText(_translate("Calculator", ")"))

class MainWindow(QtWidgets.QMainWindow, Ui_Calculator):
    def __init__(self):
        super().__init__()
        self.setupUi(self)

        self.action_plus = 0
        self.action_min = 0
        self.action_mult = 0
        self.action_div = 0
        self.action_dot = 0

        self.btn_debug.clicked.connect(self.debug)

# зачем два раза ? --------------------------------------> vvv  vvv  ? <----
#        self.btn_zero.clicked.connect(lambda: self.visual("0", "0"))
        self.btn_zero.clicked.connect(lambda: self.visual("0"))
        
        self.btn_1.clicked.connect(lambda: self.visual("1"))
        self.btn_2.clicked.connect(lambda: self.visual("2"))
        self.btn_3.clicked.connect(lambda: self.visual("3"))
        self.btn_4.clicked.connect(lambda: self.visual("4"))
        self.btn_5.clicked.connect(lambda: self.visual("5"))
        self.btn_6.clicked.connect(lambda: self.visual("6"))
        self.btn_7.clicked.connect(lambda: self.visual("7"))
        self.btn_8.clicked.connect(lambda: self.visual("8"))
        self.btn_9.clicked.connect(lambda: self.visual("9"))

        self.btn_bl.clicked.connect(lambda: self.visual("("))
        self.btn_br.clicked.connect(lambda: self.visual(")"))

        self.btn_plus.clicked.connect(lambda: self.visual("+"))
        self.btn_min.clicked.connect(lambda: self.visual("-"))
        self.btn_mult.clicked.connect(lambda: self.visual("*"))
        self.btn_div.clicked.connect(lambda: self.visual("/"))
        self.btn_dot.clicked.connect(lambda: self.visual("."))

# ?        vvvvvvvvvvvv <---- нет такой кнопки <----------------------- # ???
# ?        self.btn_del.clicked.connect(self.delete)
        self.btn_c.clicked.connect(self.delete)    # ? наверное вы хотели # ???
        
        self.btn_proc.clicked.connect(self.procent)
        self.btn_eq.clicked.connect(self.results)

# ?     vvvvvvvvvvvvvvvvvv <---- что это <----<----<----<---- # ???
        self.input_symbols = ""
        self.action = 0

    def num_handler(self, num1, num2):
        self.input_symbols = str(self.input_symbols)
        num1 = str(num1)
        num2 = str(num2)
        print(f"Нажато: {num1}")
        if self.action == 0:
            self.action = 1
            self.display.setText(num1)
            self.input_symbols = num2
        else:
            self.display.setText(self.display.text()+ num1)
            self.input_symbols =+ num2

    """ """
    def num_in_input_symbols(self, symbol):
        self.input_symbols = str(self.input_symbols)
        symbol = str(symbol)
        if self.action == 0:
           self.input_symbols = ""
           self.input_symbols = symbol
           self.action = 1
        else:
            self.input_symbols = self.input_symbols + symbol
        print(f'Натиснуто: "{symbol}" ')

    def visual(self, symbol):
        print(symbol)
        if self.action == 0:
            self.display.setText(symbol)
            self.action = 1
        else:
            self.display.setText(self.display.text()+ symbol)
            
    """ """

    def delete(self):
        try:
            print(f'Змінна input_symbols = {self.input_symbols}')
            self.display.setText("0")
            self.action = 0
            print(f"Pressed? {self.action}")
            self.input_symbols = ""
        except Exception as e:
            print("Error:", e)
    
    def rounding(self, number):
        try:
            if number % 1 == 0:
                return int(number)
            else:
                return round(number, 8)
        except Exception as e:
            print("Error:", e)
        
    """
    def rox(self, number):
        pass

    def deg(self, number):
        pass
    
    def basp(self, num):
        pass
    
    def pi(self):
        pass
    """

    def procent(self):
        try:
            num = self.display.text()
            if num.find("+") == -1 and num.find("-") == -1 and num.find("*") == -1 and num.find("/") == -1:
                p1 = float(num)
                p2 = p1 / 100
                self.input_symbols = p2
                p2=str(p2)
                p2 = p2.replace(".", ",")
                self.display.setText(p2)
            else:
                self.action = 0
        except Exception as e:
            print("Error:", e)

    def results(self):
        print(f'1 self.input_symbols = {self.input_symbols} <---- что это ?') #

        try:
# ?                    vvvvvvvvvvvvvvvvvv <---- что это <----<----<----<---- # ???
#            r1 = eval(self.input_symbols)      
            r1 = eval(self.display.text())                       # наверное так ???
            
            r2 = self.rounding(r1)                               # ???
            r2 = str(r2)                                         # ???
            r2 = r2.replace(".", ",")
            self.display.setText(r2)
            self.action = 0
        except Exception as e:
            print("def results(self): Error:", e)

    def debug(self):
        print(f'''
×--------------------------------------------×
 self.display.text() = {self.display.text()}
 self.input_symbols  = {self.input_symbols}
 self.action         = {self.action}
--------------------------------------------×''')


if __name__ == "__main__":
    import sys
    
    app = QtWidgets.QApplication(sys.argv)
    
# НЕТ, это неправильный вызов.     
#    Calculator = QtWidgets.QMainWindow()
#    ui = Ui_Calculator()
#    ui.setupUi(Calculator)
#    Calculator.show()

# Это ПРАВИЛЬНЫЙ вызов.
    calculator = MainWindow()                                   # !!! +++
    calculator.show()                                           # !!! +++
    
    sys.exit(app.exec_())