We're so sorry to hear that you're having trouble with your ZF8 flip and the Android 12 upgrade. Please try to:
Verify if the hotspot can function normally in Safe mode. If it does, then the problem may be caused by 3rd party app.
If that doesnt work, I recommend that you backup your personal data and do a factory reset. Please come back after doing so and let me know if your issue persists, so that I can report it.
Also, what mobile carrier are you using?