TLDR: Valve/Steam has never issued a general warning to users about the frame‑pacing/timing‑logic issues in certain games that make them effectively unplayable or unbeatable on SteamOS despite “running.”
-Not in patch notes, Proton release notes, Deck Verified criteria, store‑page warnings, and not in any public communication.

They do not test for timing bugs, broken physics, or unstable frametime behavior. Valve has never warned users about games that “run” but have broken timing logic under Proton/SteamOS. Major issues arise when there’s physics tied to uncapped framerate, games that rely on Windows-specific timing APIs, games that behave differently at 40/60/90 Hz and games where frame pacing instability causes input desync or impossible difficulty spikes.

Valve does not mark these games as “Unsupported,” even though the gameplay is functionally broken.

If the game launches and renders frames, Valve considers it “working.” Even if the frametime graph looks like a seismograph, the game’s logic runs too fast or too slow, boss fights become impossible, rhythm/timing games desync, cutscenes skip or break scripting, or a time trial becomes unbeatable mid-game.

No warnings. No labels. No store‑page notices.

Valve won’t even tell you, "this game runs poorly on SteamOS, is broken under Proton, or “works better on Windows”. If you want to find problems, you need to look at the fixes, but there are no ‘heads ups’.