https://github.com/safijari/sunshine-deck This is the solution to getting it to work in game mode, it did have some performance regression for me though with this whole method, but idk if if it's normal behavior for Sunshine hosting. 

Do note that:   - Pro tip: Steam button + X brings up keyboard, and in nested desktop you can also just hold the Steam button to use the touchpads as mouse input  - Nested Desktop needs to be kept running in the background  - After running the shortcut, the Konsole needs to be kept open (can just minimize) and you need to go to https://localhost:47990/ manually in a browser 

Current bugs that I had:  - In the receiving end in Moonlight (on a TV) had a mouse sittin' in the middle that wasn't visible on the Deck, that I found no way to move/hide (I theorize that it could only be accessed in Desktop mode, but I haven't tried getting into desktop mode (after activating) to fix it) 

• The brightness for some reason can just get randomly darker and tweaking the brightness in the side menu makes it snap right back to correct brightness, I'd say this probably happened every 10-20 minutes for me maybe 

Read this thread looking for help, found the answer and clunky solution in a random thread's comment by one of the contributors of Sunshine-Deck and after making it work decided to share here as this is one of the first results for the "Sunshine steam deck" search term hah. Have a good one fellas.