my iphone is frozen in an app? can't leave the app

See steps 4 and 5 of that procedure (shown below) from If your iPhone won't turn on or is frozen - Apple Support

On your iPhone 8 or later, including iPhone SE (2nd generation)

1. Press and quickly release the volume up button.
2. Press and quickly release the volume down button.
3. Press and hold the side button until you see the Apple logo.
4. If your phone doesn't turn on, follow these steps to check your hardware and charge your phone. You might need to charge for up to an hour.
5. If your phone still doesn't turn on, contact Apple Support.

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

The reset quickly press the up volume, down volume and hold the side button for 45 seconds until it powers off did not work on iPhone XS. The Eufy Security app has frozen the phone and I cannot use it for anything. I have a medical device app on my phone that provides critical alerts for a family member. This is dangerous and I've never had an app or my phone lock like this before.