I use the Steam Link app on my desktop to use keyboard + mouse on the Deck. For content from Epic, GOG, and Amazon I find Heroic Launcher to be the easiest since it’s a native Linux app and has a simple “add to Steam” button. For emulation, I use Emudeck, for everything else I use Bottles or Lutris.

No, foveated rendering doesn’t need the game to support it I use it all the time

It may be possible to run VR extremely well on the Steam Deck’s APU if Valve uses eye-tracked foveated rendering.