Personal Hotspot crashed, now unavailable
Personal hotspot only depends on the carrier and the OS of the device.

Assuming you have a backup (and it won't get overwritten during testing and activation of your newly wiped phone), you can restore the phone and set it up as new.

If that fixes the issue - you can then know it was software corruption. You'll have to decide if you want to slowly delete things on the phone after restoring from your backup or just start new and set it up again from zero, but you'll have determined that the carrier settings and the hardware are working.

Conversely, if it fails after a new setup - focus on hardware and the carrier for support.