Odd. I installed Joplin today on my Debian 12.6 (it was updated yesterday from 12.5) instance and it seems so far to work fine. It was installed from the software app store in Debian 12 as a Flatpak not from a script as indicated by the OP.
Joplin 2.14.22 (prod, linux)
Client ID: 2e59fec76c294915b02e77af4ab4d3ba
Sync Version: 3
Profile Version: 46
Keychain Supported: No
My only niggle is that I use dark mode but have been unable to invoke dark mode in the app (if someone has advice on this, would be useful).