Yes this is the same issue I’ve noticed. I’ve been playing Vampire Survivor exclusively for some time so I’m not sure if the problem is game specific or SteamOS. Probably the latter. I can run a different game later and see or maybe you can let me know.
I’ve noticed a black screen after exiting a game lately but just thought it was a problem with the specific game. I have to press the back button to get out of it and back to where you’d normally land after exiting a game, the game selection page/menu from the library in steam (there’s probably a better name for it).
It was harder than it should have been to find the GitHub page but here it is. I linked to the issues list. Seems like it’s got a quite a few. Maybe somebody will pick the project up.
For whatever reason, the interface was difficult to navigate, jumping up and down, but once I got it on the Quick Settings I was able to rearrange the controllers.