Honestly Valve needs to have a policy for this. If a game that once worked on Steamdeck and now no longer works after publisher intervention then refunds need to be issued. I have BF2042, BFV and BF1 and 1 was the LAST one I could still play on Linux. Now I have 3 digital paperweights that I can't play anymore. I want my money back.
It doesn't just do nothing. They know for sure it does nothing, is not theoretically capable of doing more than nothing to prevent cheating, and that it is a giant security hole.
They just don't care, because it lets them install a rootkit on your computer.
Maybe Valve needs to stop pushing updates for things they certified working until they certify the update won't break them.
Never understood why Steam forces updates, but this would be a very good reason for them to do a 180 on it and let customers choose the version they want instead of forcing an update to the latest.
This is why I don't see Proton as a substitute for proper support. Because if they don't actually support the platform, they could break it at any time and say you're outta luck.