Edit: An update just came through and games now launch from game mode without issue. Strange. I suppose I may have not rebooted after adding the conf file to specify the display output, not sure if that could also have fixed it.
I just installed bazzite yesterday. Device is a GPD Win 3 which has an Intel GPU. Everything works, except all 5 games I’ve tried fail to load properly when launched in Gaming Mode. 4 of them give different errors, all related to being unable to create or initialize a video device. One opens with a black screen, but I can hear audio.
All 5 games launch and play just fine if I launch them from Desktop Mode instead. I tried changing display settings to Windowed mode while playing in Desktop Mode and relaunching in Gaming Mode, but they still do not open. I also created a config file similar to what is needed for HTPC config to specify the output display port, just in case that was wrong, and still get the same errors in Gaming Mode.