And then, as a Linux user, you can just return any game you like, past the return window, by marking 'doesn't work on my system ' in the return wizard.
Sad thing that often the games that have the 15% performance hit are the ones most demanding of your hardware. It's also wierd playing some games on Linux, because clicking both left and right mouse button causes a middle click.
The most common reasons are requires using the on-screen keyboard and small fonts. Some playable games are completely fine: Occasionally I find a game that only requires using the keyboard once or twice but is still marked 'playable'.
Other than that, I have found that lots of games which aren't "Verified" play perfectly, and some games which are "Verified" don't launch at all (because Valve said 'hey! it works!', gave it the Verified badge, and then a month later the developers pushed out an update for the game which broke something for Steam Deck users).
Essentially, complete non-issues most of the time.
Game breaking bugs are rare in playable titles from what I've seen.
The majority of games I play on SD are "only" playable and it's still a great experience.
Forza Horizon 4 is Playable rather than Verified because of the Xbox Live sign in window at the start, but after that goes away it's flawless.
Playable usually means some text is too small or you need to enable the SteamOS virtual keyboard for some bits.