>I gather that having the games installed somewhere outside of steam's /home/ directory was not jiving with flatpak's security model. It took some non-trivial editing (thanks, flatseal) to finally let the Steam flatpak be able to write outside of its own directory and install the games.

I think flatpak could use a built in notification method of some sort to add exceptions to paths it's allowing access to, though I imagine it would still require effort on the application's part which maybe would never happen (especially with steam using its own custom file browser)

>At last check in, I still can't launch CS:Go, because of some backend problem while trying to play the opening movie

I've had no such issue (and it's worth noting the -novid launch option), but regardless valve still treats Linux as a second class platform despite the steam deck which is fairly disappointing.

The issue I do have is that the new overlay will crash cs:go in openGL mode and Vulkan mode has massive stutters.

I'm optimistic CS2 will be better, but to be determined.