You can use gamescope with anything, it’s a micro compositor. You can add it to the launch parameters in steam, lutris has an option to start games with gamescope, or you can simply open the game with gamescope and wine from the terminal.
Gamescope is great to use even on desktops, it runs the games in its own little shell which is particularly good for compatibility with old games where you can change stuff like resolution, fullscreen, keyboard layout… without impacting your distro.
The layout is just gnome, pretty sure you can change the DE if you want to, and yeah it does look like android which isn’t necessarily a bad thing considering desktop usage is getting replaced by mobile.
Steam and the other loaders (lutris, bottles…) take care of all the compatibility stuff just fine; the tweaks are actually the ones that can be bothersome to get, not that the performance difference matters much anyways…
Wait for one month for the new GPUs to come out, wait for the drivers to catch up, wait for the benchmarks… Or just buy a tried and tested GPU right now.