Sometimes the screen flickering problem you can try reconnect the screen flex cable, cause the flex cable may be loosen when accidentally drop or hit.
You can try to power off your phone and tear it down, check whether the screen flex cable is loosen or not,
or you can go to the Motorola service center for help.
If the methods above can not fix the screen problem, then you should turn to the hardware solution: change a new screen. Is it hard to repair it? [https://www.youtube.com/watch?v=v6Bi4b-kPK0&t=46s|Here] we also provide a video repair guide for XA Ultra screen replacement.