unable to turn off iphone xr

hey there!!

1. Quickly press and release the Volume Up button.
2. Quickly press and release the Volume Down button.
3. Press and hold the Side button until the Apple logo appears, then release the Side button.

Try doing a hard reset by quickly pressing/releasing the volume up button, then the volume down button, then press power until you see the Apple logo on the screen.

https://support.apple.com/en-us/HT201559

https://support.apple.com/en-us/HT201412