Some phones resist powering off to try to help you recover your device.
Many phones will trigger FRP (factory reset protection) if you manage to factory reset it from recovery. Then you'll be asked for the password to the Gmail account previously registered on the phone.
Sometimes FRP bypass is possible. Many methods utilize glitches.
Find my device is great. I've used it before with mixed results. Sometimes if only to confirm where you lost it. Theft-wise, obviously ymmv, but if you just misplaced it, having it make a sound can be super helpful.