My phone isn’t turning off but I’m receiving notifications

• 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.

Have you done it very carefully and precisely? If it doesn’t work your phone has a hardware problem. Contact Apple to discuss repair options→Apple - Support - Service Answer Center

Definitely a hardware problem, then.

It means that some component in the phone is broken, either physically or electronically.