My iPhone 10 locked up hard a few days and I couldn’t get it to turn off using the standard method.
After some digging, I found a new trick that I guess is implemented at a lower level: press and release volume up, then volume volume down, then press and hold the main button until it powers off.
After some digging, I found a new trick that I guess is implemented at a lower level: press and release volume up, then volume volume down, then press and hold the main button until it powers off.