After countless of trial and error.
I was not able to get MSFS 2020 Anniversary Edition Standard to run on steamdeck latest SteamOS 3.5.7
Tried the following launch option:
gamemoderun %command% PROTON_USE_DXVK=1 -FastLaunch
but still presented with unlimited loading black screen. Where the round spinner will spin for a while then hang till nobody business.
Tried multiple Proton Compatibility Runtime: (eg, Proton Experimental, Proton Latest, Proton GE-8) still was unable to get it running as well.
Also tried Proton Experimental - Bleeding Edge Beta, was out of luck as well.
From Proton DB, Seems like everyone able to launch with just Proton Experimental and “-FastLaunch” Launch option.
Not sure where i did wrong.
Might want to try and reinstall. Maybe a third party install happened and you did not know it. These can crash the game pretty hard.
I have -fastlaunch and proton experimental. Running at medium graphics 25-35fps. No problems.
Custom settings for my preference is everything on low with clouds on high. This seems to give me the best feel at 30fps always.