iphone Face ID can not be activated, it is not real damaged, or not working, jut is hibernate or Self protection from apple design, the new face id flex cable just wake up it
just re-programming the underlying data (SN BT WF Color Country….. others information), not the file data JC pro1000s for iphone nand or eeprom ic or Chip, not the baseband cpu or the others ic
Disconnect the screen, check the whole screen for any faults. Disconnect the battery, wait for a while the reconnect the battery and then reconnect the screen, perhaps, it is FPC socket connection