Thank you Deggie! My 13 Pro started having a weird screen malfunction, I could hit the side button and the screen would turn on/off, but the graphics were so glitched, fuzzy, and moving strangely - I certainly could not swipe to unlock and face recognition was not working, therefore "swiping" to turn off my phone the old fashioned way was not working.
I didn't even know this was a possibility - your suggestion of (somewhat quickly/normal speed) pressing the volume up button, releasing, then the volume down button, releasing, then pressing and holding the side lock button did force my iPhone to restart!
Thankfully the screen is working normally (for now) let's hope it stays that way - there shouldn't be anything wrong with the phone given it's brand new - annoying!