

It’s dropping as in “experiencing a fall in numbers” (back to normal levels) not as in “removing from support” nor as in “delivered to the world”
They may have removed it from the reporting or corrected for some previous change in reporting methodology.
Can confirm, it’s fine. There’s some variability of course but taken as a whole the environment is comparable in terms of performance. As long as you’re not playing AAA competitive games that have anti-cheat you are going to be fine with few exceptions. And there are plenty of examples where the proton experience works better than the native.
Check protondb to get a realistic idea of how well games will work.