I created a custom bazzite image based on bazzite-deck with your custom kernel (as of commit 15bc7f8). The OS is meant to boot into the steam 'game mode' by default, however upon booting I am immediately put into KDE. Attempting to enter game mode results in a temporary black screen, and then being put back in KDE. I have attached a dmesg log below.
https://pastebin.com/afFEkt3N
Not sure if this is out of your reach and a result of bazzite's reliance on it's custom kernel, but figured I could create an issue.