Honestly, because troubleshooting gets annoying for me when I want to play a game, I have made a brain-dead algorithm for how to play games on the deck, and it looks like this:
Do I want to buy it on Steam? If not,
Does it run in Windows? If yes, just download and install in Windows PC, and then (Warpinator) it into the deck. Add shortcut to steam, use latest stable proton. That’s it. You’re done.
W-wait… It doesn’t run natively on Windows? (Old af games like Touhou 6). Just Bottles it, and finagle with the setup a bit, that’s gonna take some effort.
As a general rule, proton is a beast, and I have stopped bothering with Linux native piracy entirely.