In current dev, only a quarter of the content of a Web Engine view is painted on the screen (see attached screenshot). When scrolling, the view, the content in that quarter does get updated, so it seems the rendering is correct.

Both widgets and quick APIs are affected, so this can be reproduced with simplebrowser or quicknanobrowser.

Seen so far on dev/102-based and arm64-macOS, verifying currently that it is also a problem with 6.4.