My goal isn’t to devolve into a discussion about reactive framework performance. My core question is, “Is there a non-reactive layer that we can jump into, similar to the render object layer in Flutter?”

Yes, https://github.com/JetBrains/skija 😂

lol

Not really, no, we do not use a VDOM in the same sense as something like React or Flutter. That was one the mistakes we made back when my old team was building React.js and one which I pushed very very hard to avoid in Compose (ie. allocations). That's one of the reasons we are a compiler plugin instead of a runtime library.

Idk if compose is suitable for game rendering, but compose is great for managing trees of objects in general (core compose has nothing to do with ui or graphics). If your game uses a tree of entities, scene graph, etc, you could use compose to write your game logic and still use a different rendering engine to actually draw the pixels.