Hi! Professional android dev here who has done some work on migrating an app to foldable:
Apps don’t guess. If they’re using XML they make specific layouts for a given width of screen.
If they’re using compose it’s even easier: the entire UI library is built for adaptive layouts. The main issue is a lot of apps are not in compose UI (or not entirely) - and material 3 has excellent components but it’s even less widely used.
Tldr: tech debt
A potential cause of the wonkiness is explicitly setting resizeableActivity=“false” in the app manifest.