Cone example in QVTKRenderWindowInteractor not showing up

Tested as follows on Kubuntu 20.04 (Python 3.8):

estan@edison:~$ python3 -m venv testenv
estan@edison:~$ source testenv/bin/activate
(testenv) estan@edison:~$ pip install vtk pyqt5
Collecting vtk
  Using cached vtk-9.0.1-cp38-cp38-manylinux2010_x86_64.whl (103.4 MB)
Collecting pyqt5
  Using cached PyQt5-5.15.0-5.15.0-cp35.cp36.cp37.cp38-abi3-manylinux2014_x86_64.whl (76.6 MB)
Collecting PyQt5-sip<13,>=12.8
  Using cached PyQt5_sip-12.8.1-cp38-cp38-manylinux1_x86_64.whl (293 kB)
Installing collected packages: vtk, PyQt5-sip, pyqt5
Successfully installed PyQt5-sip-12.8.1 pyqt5-5.15.0 vtk-9.0.1
(testenv) estan@edison:~$ python3 testenv/lib/python3.8/site-packages/vtkmodules/qt/QVTKRenderWindowInteractor.py 
PyQt5

At this point nothing happens, the window is not showing up.

I seem to remember this working out of the box in the past.

@dgobbi