A quick test of Forza horizon 1 on the steam deck running steam OS. This is with xenia canary and emudeck. I changed the following settings:

xeniacanary.config.toml: gpu="d3d12" mount_cache=true
mount_scratch=true

change this on Emulation/tools/launchers/xenia.sh: PROTONVER=" Experimental" to: PROTONVER="GEProton815"

thank you ‪@PixelacosGameplaysTV‬ for the settings

without these The game launched but as soon as you got into the opening race it was just a black screen. I would definitely call this playable, but the frame times aren't the greatest. let me know if you have any questions, I'm still kind of new to Linux and emulation but I will try to help.