Game runs great on the Deck, and supports 16:10 display aspect ratio out of the box.
With below listed settings I get anywhere between 55-60 FPS, but going down to 40Hz/FPS will save you tiny bit of battery while making the game run smoother and rock steady at 40 FPS.

Motion Blur: High (Set to whatever you like)
Depth of Field: Valid
Model Detail: High
Textures: High
Texture Filtering: High
Shadows: Medium
Lighting: High
Post Processing: High
Effects: High
Ambient Occlusion: High

Half Rate Shading: Garbles up text and makes a lot of textures look like garbage, do not use.
TDP Limit: When enabled Deck allows a maximum of 15W, which isn't enough to run the game at above mentioned settings, or even lowest settings. Yields about 15 FPS. Do not use.
Scaling filter/FSR: Broken. Setting low resolutions results in black bars, either top/bottom or entirely shrunk image that won't scale up to full size. Do not use.

Use the command the launch command MANGOHUD_CONFIG=fps_limit=40,no_display mangohud %command% to cap the FPS to 40 without using the steam limiter since it adds tons of latency, also disable vsync in game, and cap the refresh rate to 40 in the deck limiter (only the refresh rate, leave the fps to unlimited) thank me later.

In game settings : everything at "high", for the motion blur, use what you like, and again, for the lowest input lag, in game vsync to OFF.

Don't bother playing with the TDP and GPU clock settings, they don't help with this game and you can't squeeze battery life with it.