DOOM

Used this for reference: https://www.reddit.com/r/OptimizedGaming/comments/w4g8z9/doom_2016_optimised_settings/

Manual GPU Clock: 900 MHz 
Aspect Ratio: 16:10 
Resolution: 1280x800 (16:10) 
Vertical Sync: On 
Anti-Aliasing: Off 
Gamma: 2.8 
Motion Blur: Low 
Chromatic Abberation: Off 
Field of View: 90 
Graphics API: Vulkan 
Resolution Scale: 75% 
Lights Quality: Medium 
Shadows Quality: Low 
Player Self-Shadow: Off 
Directional Occlusion Quality: High 
Decal Quality: Medium 
Decal Filtering: Anistrophic 16x 
Virtual Texturing Page Size: Low 
Reflections Quality: Low 
Particles Quality: Medium 
Compute Shaders: On 
Motion Blur Quality: Low 
Depth of Field: Off 
Depth of Field Antialiasing: Off 
HDR Bloom: Off 
Lens Flare: Off 
Lens Dirt: Off 
Rendering Mode: Subjective 
Sharpening Amount: 2.0 
Film Grain: Subjective 
UI Opacity: Subjective 
Show Performance Metrics: Off 

Text is hard to read at Native 600p so it's better to set resolution to 800p and turn the rendering scale down instead. 

The guide suggested 700MHz but I suggest 900 because there is one point in the game where the framerate will suffer if you keep it at 700. 

Anti-Aliasing - TAA (1TX)

Graphics API - Vulkan

Overall Quality - Low

Resolution Scale - 75%
Leave everything else at default

Vulkan API provides far better performance compared to OpenGL. Overall quality on low will roughly approximate to base PS4/Xbox One settings and will still provide greater detail than the Nintendo Switch version.

I choose to drop the resolution scale to 75% which equates to 600p. Doing so provides a full 60fps experience while maintaining 3 hours of battery life. The 600p resolution is cleaned up nicely by the in-game TAA and remains higher than the Nintendo Switch version's resolution. Though, I'm sure you could increase the resolution to 800p at cost to battery life.

Testing was done on SteamOS 3.5 with Proton 8.

Vsync: OFF
Anti-Aliasing: TSSAA(8TX) (it's very crucial, since any other AA options or none are leading to performance lag very hard)
Graphics API: Vulkan
Resolution Scale: 80% (can be also set to prefered, minor impact on power draw tbh)
Compute Shaders: ON (for better input responsiveness)

Also don't forget to set Allow Tearing to ON for get rid of unnecessary input lag