Hi, hope my reply helps.
i was handed the iphone 11 from a family member whick they took to apple and they refused to fix,
it had a cracked screen and it was on an infinite loop out of no where.
i opened it and by disconnecting the face id module and speaker cable it let it boot back up,
i asume the face id module is bad, now im looking around to see how can i replace it, good luck.