Multi touch is broken on Proton? Deck?

So I am unsure if this is a Proton issue, or a Deck issue, but it's still an issue regardless.

The Deck is fully capable of multi touch, all 10 fingers, yet over Proton multi touch games fail, even if you add the touchscreen native option, if a Proton game requires two fingers, the deck will ignore the second. Despite this, native linux apps, on Xorg or Wayland work just fine.

This means either A. Wine/Proton lack native multitouch, and it has to be added as part of the wayland port (or maybe it could work on X? Its unclear if X actually supports proper touch events but Okular pinching just fine on the desktop leads me to believe they do.)

B. Steam input just doesn't pass two fingers to proton games.

Everything I said here is contestant in gamescope and desktop mode.

Start by reproducing the two-finger failure in a Proton game on Deck, then compare it with native Linux apps under Xorg and Wayland as described. Trace whether the missing event lies in Steam Input, Proton, or gamescope; done means identifying the responsible component and confirming two-finger input reaches the game.