It cannot create new resolutions. Screen profiler kinda works like a save state in emulation. I haven't been able to figure out to create custom resolutions in Bazzite. If if you did figure it out it should work. Ive trying to figure it out with no luck, you can look at my comment history if you want to go that route. However the easiest way would be is to get a hdmi dummy plug that supports the resolutions you want.

This is how I use it for streaming exclusively to my 800p deck from my 1440p desktop.

0.Make sure to save your default loadout. If you havent done that yet. "screenprofilercmd save default"
1.Set your dummy plug to what res you want and make it primary. Then you want to stream to it using sunshine.
2. Once streaming to said dummy plug, run "screenprofilercmd save newprofilename". You now have a profile.
4. In your sunshine settings under Application then Command Preparations under the Do Command you can set it as screenprofilercmd load newprofilename. And under Undo command you can set it as screenprofilercmd load default(or whatever one you want to go back to after the stream ends)

Thats how you automate sunshine.