Контекстное меню на PySide2

Как вариант

import sys
from random import randint
'''
from PySide2 import QtCore, QtGui, QtWidgets
from PySide2.QtCore import Qt
'''
from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5.Qt import *

#from UI_test import Ui_Form
class Ui_Form(object):
    def setupUi(self, Form):
        Form.resize(800, 500)
        self.layout = QtWidgets.QHBoxLayout()
        self.layout.setContentsMargins(0, 0, 0, 0)
        self.listWidget = QtWidgets.QListWidget()
        self.layout.addWidget(self.listWidget)
        self.stackedWidget = QtWidgets.QStackedWidget()
        self.layout.addWidget(self.stackedWidget)
        self.listWidget.currentRowChanged.connect(
        self.stackedWidget.setCurrentIndex)

        item1 = QtWidgets.QListWidgetItem(QtGui.QIcon('Ok.png'),'CamSettings', self.listWidget)
        item2 = QtWidgets.QListWidgetItem(QtGui.QIcon('im.png'),'Explore', self.listWidget)

        item1.setSizeHint(QtCore.QSize(10, 60))
        item2.setSizeHint(QtCore.QSize(10, 60))

        item1.setTextAlignment(QtCore.Qt.AlignCenter)
        item2.setTextAlignment(QtCore.Qt.AlignCenter)

        label1 = QtWidgets.QLabel('Это страница 1')
        label2= QtWidgets.QLabel('Это страница 2')
        label1.setAlignment(QtCore.Qt.AlignCenter)
        label2.setAlignment(QtCore.Qt.AlignCenter)
        label1.setStyleSheet('background: rgb(%d, %d, %d); margin: 50px;' % (
        randint(0, 255), randint(0, 255), randint(0, 255)))
        label2.setStyleSheet('background: rgb(%d, %d, %d); margin: 50px;' % (
        randint(0, 255), randint(0, 255), randint(0, 255)))

        self.table_cubes = QtWidgets.QTableWidget()
        self.table_cubes.setColumnCount(1)
        self.table_cubes.setObjectName('tableCubes')
        self.table_cubes.setHorizontalHeaderLabels(['Название куба'])
        header_class = self.table_cubes.horizontalHeader()
        header_class.hide()
        header_v_cube = self.table_cubes.verticalHeader()
        header_v_cube.setStyleSheet(' background-color: #232939;')
        self.table_cubes.setFixedWidth(310)
        self.table_cubes.setFixedHeight(330)
        self.table_cubes.setColumnWidth(0, 200)
# -       self.table_cubes.contextMenuEvent = Form.contextMenuEvent
        
        first_panel_left = QtWidgets.QVBoxLayout()
        first_panel_left.setAlignment(Qt.AlignTop)
        first_panel_frame_left = QtWidgets.QFrame()
        first_panel_frame_left.setMinimumWidth(200)
        first_panel_frame_left.setLayout(first_panel_left)
        first_panel_right = QtWidgets.QVBoxLayout()
        first_panel_right.addWidget(self.table_cubes)
        first_panel_right.addStretch()
        first_panel_frame_right = QtWidgets.QFrame()
        first_panel_frame_right.setLayout(first_panel_right)
        main_first_box = QtWidgets.QHBoxLayout()
        main_first_box.addWidget(first_panel_frame_left)
        main_first_box.addWidget(first_panel_frame_right)
        first_container = QtWidgets.QWidget()
        first_container.setLayout(main_first_box)
        self.stackedWidget.addWidget(first_container)
        self.stackedWidget.addWidget(label2)
        Form.setLayout(self.layout)
        
        
class App(QtWidgets.QWidget):
    def __init__(self, parent = None):
        QtWidgets.QWidget.__init__(self, parent)
        self.ui = Ui_Form()
        self.ui.setupUi(self)

# +++ vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv        
        self.item = None
        self.ui.table_cubes.installEventFilter(self)                             # !!! 
        self.ui.table_cubes.setRowCount(3) 
        self.ui.table_cubes.setItem(0, 0, QtWidgets.QTableWidgetItem('Hello'))        
        self.ui.table_cubes.setItem(2, 0, QtWidgets.QTableWidgetItem('World'))          

    def eventFilter(self, source, event):
        if event.type() == QEvent.ContextMenu and source is self.ui.table_cubes:
            menu = QMenu()
            menu.addAction('Action 1')
            menu.addAction('Action 2')
            menu.addAction('Action 3')

            menu.triggered.connect(self.selected)                               
                    
            if menu.exec_(event.globalPos()):
                self.item = source.itemAt(event.pos())
            return True
        return super().eventFilter(source, event)
        
    def selected(self, q):
        self.q = q.text()
        QTimer.singleShot(10, lambda: print(f'{self.item.text() if self.item else None}: {self.q}'))
# +++ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    window = App()
    window.show()
    sys.exit(app.exec_())