Xeshra: I mean, Linux users keep telling me, they can get to run any game ever. But if they have to rely on Proton to make it happen... it does not sound tasty to me, as Linux will not be free.
Proton is nothing but a fancy name for a couple of open source tools (as far as I know), like Wine, DXVK, D3DVK etc.
If memory isn't failing too much, developer of DXVK (DX to Vulkan translation layer) got hired by Valve but still release the code.
You can pretty much apply the translation layer yourself or use automated tools like Lutris, Bottles or PlayonLinux without ever touching Steam.
However, adding a non-Steam game to Steam library and apply the Proton translation layer works fine as well.
Zimerius: Is that right? Guess it needed the new UI to become more visible to some
The old UI was very cumbersome and outdated, glad they changed it. It makes adding non-Steam games on the Steam Deck a breeze instead of a chore.