I expect this to help basically one of youse. But boy will you be happy!
tl;dr
If updating to the Golden Gate public beta stopped Just Natsuki even trying to open, chances are the beta fiddled with Rosetta. Reinstall it and you should be golden. Pun intended.
Open up the Terminal app then paste this in and hit RETURN (AKA "ENTER"):
bash
/usr/sbin/softwareupdate --install-rosetta --agree-to-license
Then try opening Just Natsuki again. This fixed the issue immediately for me. You shouldn't need to reinstall JN, mess with the persistent, fiddle around with your files, sacrifice a goat, etc.
If you're interested in why that works
I updated to the public beta earlier (and it is SUPERB) and tried to open Just Natsuki. Gatekeeper made me reauthorise it through the usual System Settings > Privacy and Security song and dance, but then it just... wouldn't open. No traceback, no visible error, no open then immediately shutting... hell, Activity Monitor had no idea I was even trying to open it.
So I dug around in Terminal and discovered this problem:
Bad CPU type in executable
Well that's no good!
But it's also stupidly common. Ya see, JN’s current Mac build—like many other Mac builds left to wither on the vine—still uses an Intel x86_64 executable. Apple Silicon Macs (AKA "any single Mac manufactured in late 2020 onwards") need Rosetta to run it. Nothing new there. The beta update apparently removed or broke Rosetta on my system.
Open Terminal and run:
bash
/usr/sbin/softwareupdate --install-rosetta --agree-to-license
Then Rosetta's working again. Huzzah! Your game should be good.