I've put about 4-5 hours into this game on my steam deck OLED at a pretty solid 40FPS.

I play on the medium preset with some slight changes to the graphical settings.

Firstly, I lower the resolution to 1152x720. This allows the game to use the full 16:10 screen while not making it super blurry. It allows to cut down on the GPU usage to reduce lag spikes. If you'd like you can activate FSR in the steam menu to get a bit of a crispier image. That is what I do and I haven't noticed any lag spikes with it enabled but if you do notice you need the performance you can keep it disabled, it doesn't effect visuals much. I haven't experiemented much with keeping native resolution with my other changes, feel free to try it out.

Next I disable all motion blur and depth of field. These settings affect performance a lot. All other settings I keep the same as comes with the medium preset.

There is a patch which enables the game to use DXVK to improve the performance and GPU usage. This works on PC however on Steam Deck proton already makes games use DXVK so it has no affect on performance with the Steam Deck.