an app on xr won't close can't power off either

Follow the steps in this support document for if your device is frozen. If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support

If you cannot do a forced restart or connect it to your computer and put it in recovery mode and restore it you must have a serious hardware failure. Click on the Contact Support link on the top right of this page to start the service process.

Settings > General > (scroll down to) Shut Down

You can’t even do a force restart from the article ChrisJ4203 sent?

Then once you’ve worked your way through all the “If...” steps in the article ChrisJ4203 attached, you work your way down to the “Contact Apple Support” area.