If recommend reading the quote from unity explaining it:

One thing I can talk about now is that we’re bringing official Steam support into Unity. Now, I know you’ll say “But I already ship games to Steam” and that’s true. Thousands of developers have had success on Steam with Unity. The thing is, prior to Platform Toolkit, we’ve never actually officially supported Steam in the past. It’s always been up to developers to integrate Steamworks themselves, and publish and support their titles on that platform historically.

And on Steam Deck, many of you have been finding success with Proton. But I think we can do better with a native solution. So, as I mentioned before our strength is highly performant native runtimes. So moving forward we’ll provide not just build targets for Steam but also Steam Deck and the upcoming Steam Machine. We’ll also look to make targeted enhancements to our Linux runtime to provide native performance increases and remove the need for developers to rely on Windows through Proton.

And look, as great as Proton is, it’s simply something we don’t have any degree of control over or ability to support. And we’ve actually made some native improvements to the Linux player that targets the Steam Deck hardware. Offering a potential improvement in performance over a build running on Proton and that’s actually available today.

Godot is getting sooo good. Fuck unity and unreal.

UI scaling still has some rough edges on Linux in general. For example when running X11 applications under Wayland. Or when using multiple screens with different scaling.