Adding to this, setting the game to use the D3D11 renderer with the launch option +r_rhirenderfamily d3d11 fixes the slowdown but also pegs a thread to 100% CPU usage.
Please retest, the game should be working better on game mode now
Nothing extracted yet.
Compatibility Report
System Information
I confirm:
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Symptoms
Very odd performance behavior through Game Mode. It feels like the game is capable of reaching 90fps, but is being held back. With various seemingly random fps drops at places you do not expect it. With vsync turned off and on.
but if you then go to Desktop Mode, turn off vsync and set the ingame cap to 90 fps. The game runs absolutely buttery smooth. So the Deck is absolutely capable of running the game with ease, there might just be a proton issue .
Reproduction
Just by playing the game in Game Mode and then comparing it to the performance in Desktop Mode.