iPhone XS Max - Black dot

Try Some Troubleshooting?

1. Restart:  Press On/Off button until the Slide to Power Off slider appears, select Slide to Power Off and, after It shuts down, press the On/Off button until the Apple logo appears.
2. Reset:  Press the Home and On/Off buttons at the same time and hold them until the Apple logo appears (about 10-15 seconds).
3. Restore:  Connect your iPhone to iTunes on your computer, backup, and then select Restore to Factory.
4. How to erase your iOS device & then set it up as a new device or restore it from backups.

If all else fails then make an appointment at the Apple Genius Bar for service. If you need to find an Apple Store - Find a Store - Apple. If you did not purchase it from Apple then you will need to look to the vendor for service or How to find your nearest Apple Authorized Service Provider (AASP) or Distributor (AAD).