Добавление QLineEdit в QLineWidget

Не уверен что правильно понял вас, но предложу попробовать как вариант:

import sys
'''
from PySide6.QtCore import (QCoreApplication, QDate, QDateTime, QLocale,
    QMetaObject, QObject, QPoint, QRect, QSize, QTime, QUrl, Qt, Signal)
from PySide6.QtGui import (QBrush, QColor, QConicalGradient, QCursor,
    QFont, QFontDatabase, QGradient, QIcon, QImage, QKeySequence, 
    QLinearGradient, QPainter, QPalette, QPixmap, QRadialGradient, QTransform)
from PySide6.QtWidgets import (QAbstractItemView, QApplication, QGridLayout, QListWidget,
    QListWidgetItem, QMainWindow, QPushButton, QSizePolicy, QWidget)
'''

from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5.Qt import *


#from ListTest import *
class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        if not MainWindow.objectName():
            MainWindow.setObjectName(u"MainWindow")
        MainWindow.resize(631, 297)

        self.centralwidget = QWidget(MainWindow)
        self.centralwidget.setObjectName(u"centralwidget")
        self.gridLayout = QGridLayout(self.centralwidget)
        self.gridLayout.setObjectName(u"gridLayout")
        
        self.listWidget = QListWidget(self.centralwidget)
        self.listWidget.setObjectName(u"listWidget")
        font = QFont()
        font.setFamilies([u"Times New Roman"])
        font.setPointSize(14)
        font.setBold(False)
        font.setItalic(False)
        self.listWidget.setFont(font)
        self.listWidget.viewport().setProperty("cursor", QCursor(Qt.PointingHandCursor))
        self.listWidget.setFocusPolicy(Qt.NoFocus)
        self.listWidget.setLineWidth(1)
        self.listWidget.setVerticalScrollBarPolicy(Qt.ScrollBarAsNeeded)
        self.listWidget.setHorizontalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
        self.listWidget.setAutoScroll(False)
        self.listWidget.setAutoScrollMargin(16)
        self.listWidget.setSelectionMode(QAbstractItemView.MultiSelection)
        self.listWidget.setSelectionBehavior(QAbstractItemView.SelectItems)
        self.listWidget.setVerticalScrollMode(QAbstractItemView.ScrollPerPixel)
        self.listWidget.setHorizontalScrollMode(QAbstractItemView.ScrollPerPixel)
        self.listWidget.setSpacing(4)
        self.listWidget.setWordWrap(True)

        self.gridLayout.addWidget(self.listWidget, 0, 0, 1, 1)

        self.pushButton = QPushButton(self.centralwidget)
        self.pushButton.setObjectName(u"pushButton")

        self.gridLayout.addWidget(self.pushButton, 0, 1, 1, 1)

        MainWindow.setCentralWidget(self.centralwidget)
        self.retranslateUi(MainWindow)
        QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle(QCoreApplication.translate("MainWindow", u"MainWindow", None))
        self.pushButton.setText(QCoreApplication.translate("MainWindow", u"PushButton", None))


class Label(QLabel):
#     clicked = Signal()                              # PySide6.QtCore.Signal
    clicked = pyqtSignal()                            # PyQt5
        
    def __init__(self):
        super().__init__()
        
    def mouseReleaseEvent(self, event):
        self.clicked.emit() 
        

class MyWidget(QWidget):
    def __init__(self, num):
        super().__init__()
        
        self.flag = True
        
        self.label = Label()       
        self.label.setText(f'{num}')
        self.label.setAlignment(Qt.AlignCenter)
        self.label.setSizePolicy(QSizePolicy.Expanding, QSizePolicy.Expanding)
        self.label.setStyleSheet("background-color: #E7F7F4;")
        self.label.clicked.connect(self.onClicked)
        
        self.lineEdit = QLineEdit("lineEdit")
        self.lineEdit.setEnabled(False)
        
        layout = QHBoxLayout(self)   
        layout.setContentsMargins(0, 0, 0, 0)
        layout.setSpacing(0)
        
        layout.addWidget(self.label, 1)     
        layout.addWidget(self.lineEdit, 0, alignment=Qt.AlignRight)
        
    def onClicked(self):
        if self.flag:
            self.label.setStyleSheet("background-color: #8AD8CA;")
            self.lineEdit.setEnabled(True)
        else:
            self.label.setStyleSheet("background-color: #E7F7F4;")
            self.lineEdit.setEnabled(False)
        
        self.flag = not self.flag
        

class Test(QMainWindow, Ui_MainWindow):
    def __init__(self):
        super(Test, self).__init__()
        self.setupUi(self)
        
        self.lst = list(range(1, 21))
        
        self.print_list()

    def print_list(self):
        for i in self.lst:
            item = QListWidgetItem()                           # - str(i)
            item.setTextAlignment(Qt.AlignHCenter)
            self.listWidget.addItem(item)

            widget = MyWidget(i)                               # +++
            self.listWidget.setItemWidget(item, widget)        # +++
        

if __name__ == "__main__":
    app = QApplication(sys.argv)
    window = Test()
    window.show()
    sys.exit(app.exec())