iPhone stuck on 'iPhone Unavailable' screen

Only if you don’t have a computer to reset your iPhone. And there’s always the chance that you don’t need one at all to reset it.

Take a look at this following Support Article for instructions:

If you forgot your iPhone passcode or your iPhone is disabled - Apple Support

If you see the Forgot Passcode? Option in the bottom right, you can follow this without a computer:

If you see an iPhone, iPad, or Apple Vision Pro unavailable message or Security Lockout screen - Apple Support