I have been spinning up several new Linux virtual machines, and I discovered that VR3 isn't rendering visibly. It's still working, since you can export the rendering to the browser, but nothing is painted on the VR3 panel.
All these VMs use a recent version of Python3 with PyQt5. The PyQt5 and pyqt5-webengine versions agree with earlier VMs where VR3 is rendering normally, but I suspect there's something wrong with these binaries anyway.
Where available, I upgraded to pyqt6 and PyQt6-WebEngine-Qt6, and after the upgrade VR3 is rendering normally.