iPhone is frozen - cannot turn off, cannot reboot

Do this VERY CAREFULLY:

• Press and quickly release VOLUME UP

THEN

• Press and quickly release VOLUME DOWN

THEN

• Hold the SIDE button until an Apple logo appears (15-30 seconds), ignoring "slide to power off" if it appears

The operative word here is QUICKLY; and try it a couple of times, the timing is a little tricky.

This procedure loads a very low level ROM process and is guaranteed to work unless there is a hardware failure.

Try Force Restarting it - Force restart iPhone - Apple Support

If your iPhone won't turn on or is frozen - Apple Support

Do this VERY CAREFULLY:

• Press and quickly release VOLUME UP

THEN

• Press and quickly release VOLUME DOWN

THEN

• Hold the SIDE button until an Apple logo appears (15-30 seconds), ignoring "slide to power off" if it appears

If you HOLD it won’t invoke Siri

What happens when you try the forced restart? Do you detect any sign of life? And please not the steps for forced restart have to be done quickly and you have to hold the side button in until you see the Apple logo.

As Lawrence stated, if Force Restart really doesn't work, then the issue is with the hardware.

You'll need to contact Apple Support in this case - iPhone Repair - Official Apple Support

Tried the forced restart on my iPhone XR. Pressed volume up|down and side button. Doesn’t go to apple logo just goes to Siri???? What next?