Does the following example work for you?
(you may have to replace PySide6 if you are using different python/qt bindings)
from PySide6.QtWidgets import QApplication, QMainWindow
from vtkmodules.vtkFiltersSources import vtkConeSource
from vtkmodules.vtkRenderingCore import vtkActor, vtkPolyDataMapper, vtkRenderer
import vtkmodules.vtkRenderingOpenGL2
import vtkmodules.vtkInteractionStyle
from vtkmodules.qt.QVTKRenderWindowInteractor import QVTKRenderWindowInteractor
# every QT app needs an app
app = QApplication(['QVTKRenderWindowInteractor'])
window = QMainWindow()
# create the widget
widget = QVTKRenderWindowInteractor(window)
window.setCentralWidget(widget)
# if you don't want the 'q' key to exit comment this.
widget.AddObserver("ExitEvent", lambda o, e, a=app: a.quit())
ren = vtkRenderer()
widget.GetRenderWindow().AddRenderer(ren)
cone = vtkConeSource()
cone.SetResolution(8)
coneMapper = vtkPolyDataMapper()
coneMapper.SetInputConnection(cone.GetOutputPort())
coneActor = vtkActor()
coneActor.SetMapper(coneMapper)
ren.AddActor(coneActor)
# show the widget
window.show()
widget.Initialize()
widget.Start()
app.exec()