Anki opens but all windows are blank

[BlackBeans]

This might be of interest, since the question seems similar.

See nothing when I open Anki on Mac

Have you actually tried installing Qt, then Anki from github? From the error message I have the impression that Qt fails to locate some of its core resources (the Qt WebEngine resources), which are responsible for rendering widgets, so it is very plausible that it is the reason why the window opens, but it doesn’t render anything. Incidentally, pyqtwebengine seems to be a package on its own, so make sure it is installed when installing Qt.