Force secondary display to only show one app

I have multiple displays attached to my M1 (Sonoma 14.14.1). I'd like one of these displays to only ever display a single app - to not have other spaces on that display, and restore on reboot/unlock/(re)connection etc. I've looked around tools like BetterSnapTool, and I'm about to try an AppleScript attached to particular events. Does anybody know how I could achieve this? I'm open to solutions involving configuration, 3rd party apps, AppleScript or Swift.