When the battery gets degraded to the point where it cannot sustain peak performance, iOS throttles the phone to prevent unexpected shutdowns. Maybe your battery is too degraded and you might have turned off the throttling which is causing the phone to shut down when under load.
Tactical_Balls t1_j0tpc15 wrote
Reply to My iPhone 12 Pro randomly restarts itself every couple of days. by [deleted]
When the battery gets degraded to the point where it cannot sustain peak performance, iOS throttles the phone to prevent unexpected shutdowns. Maybe your battery is too degraded and you might have turned off the throttling which is causing the phone to shut down when under load.