From Hardlimit
The Linux OS symbol only tells you if the game is Linux native or not. Since valve released proton it is not very useful. The deck Verified/Deck Playable symbols are a far better indication of if a game will work. But even then, quite a few of the unsupported games still work on Linux overall, just less well on the deck. ProtonDB is the more definitive source of if a game will work as well as any tweaks you can do to make it run better.