DX11 with Enhanced engine. Medium settings with GPU particles on Low/Disabled, Film Grain and Contact Shadows off, and Fixed Scaling in 90. You'll need Proton GE 7.43 and activate DXVK_ASYNC=1 in launch parameters. 

No settings changed on Steam Deck itself. 

Upscaling method: FSR 2.2 - quality
Geometry quality: high
Shadow quality: medium
Texture memory: high
Particle system memory: high
Gpu particle quality: medium
Anisotropic filtering: 8x
Trilinear filtering: on
Advanced setting default except enhanced decals off

Steam Deck LCD Delta Fan 512GB Jul 2023
Warframe [Update 35.5.2]

https://steamcommunity.com/sharedfiles/filedetails/?id=3206466801
https://steamcommunity.com/sharedfiles/filedetails/?id=3206468896
https://steamcommunity.com/sharedfiles/filedetails/?id=3206469167
https://steamcommunity.com/sharedfiles/filedetails/?id=3206469378

Suprised to see nobody making a proper settings guide for Warframe here. 
Bunch of mumbo-jumbo if you ask me.
This is for best overall performance and visual clarity, battery consumption is not a priority. But for those who want to know, you get one and a half hour of playtime with a full charge on it. Enjoy!