Having a new M2 Ultra Studio, and always using 2 monitors to edit, makes this an issue close to my heart. Especially because to fix it, you must set you mac to Display have separate Spaces, which means you can’t have windows party between 2 windows and you are forced to have a dock that switches between the 2 windows (seemingly at random) and menus confusingly on both windows.

The current workaround is posted on Adobe Community from a question by Igal Hect.

From Kyle Plumadore an Adobe Employee.

I have a quick update for anyone experiencing poor playback performance on M2 Mac Studio Multi-display setups. We’ve identified an issue where disabling the MacOS system setting “Displays have separate Spaces” under “Desktop & Dock” degrades playback performance. By default this setting is enabled. We’re still working on an official resolution but in the meantime you can try re-enabling that setting as a workaround (requires system reboot to take effect) 
I have a quick update for anyone experiencing poor playback performance on M2 Mac Studio Multi-display setups. We’ve identified an issue where disabling the MacOS system setting “Displays have separate Spaces” under “Desktop & Dock” degrades playback performance. By default this setting is enabled. We’re still working on an official resolution but in the meantime you can try re-enabling that setting as a workaround (requires system reboot to take effect) 

Kyle Plumador, Adobe Employee

And with the issue not fixed in Sonoma or in Premiere, I think this is going to go on for a long time, and I HATE IT.