We have customers shipping full UI with Rive! Games have been adopting us (some cool AAA titles already in progress) and products too.
https://rive.app/game-ui
https://rive.app/blog/how-age-of-learning-uses-rive-to-a-b-t...
Incidentally, I recently opened a PR to add Metal to Godot via https://github.com/godotengine/godot/pull/88199