To perform a hard reboot on the iPhone X
- Press and quickly release the Volume Up button
- Then do the same for the Volume Down button.
- Follow up by pressing the Side button, and hold until the display suddenly shuts off — about 10 seconds.
- Keep holding the Side button and release when the device turns back onto its Apple boot screen.
This is the same process the iPhone 8 and 8 Plus use to force-restart, too.