I think you can prioritize any program for quite some time on a Mac, no need for game mode to acchieve that.
Start Photoshop.
Open a terminal.
Run ps -ef and identify which of the running processes is Photoshop. Take note of the process ID (PID).
Run renice -n -20 -p (put PID of 'Photoshop' here).
Be aware that maximum priority is set with -20 and minimum priority with +20.
nota bene: you could use nice to start Photoshop with higher priority with a shell script directly; as written renice allows to change the priority of already running processes. Boosting the bluetooth connection like in game mode seems unnecessary to me, obviously YMMV 😄
I’ve made an AppleScript, that can be saved as an app, to prioritize iMovie
AppleScript:
tell application "System Events" to set pidNumber to the unix id of process "iMovie"
do shell script "renice -n -20 -p " & pidNumber with administrator privileges
It can be adapted for any app by replacing “iMovie” with the name of the app, as displayed in Activity Monitor.
To check if the priority was changed, from Terminal: