How to unfreeze the iPhone display?

If your iPhone is frozen, either on the Home Screen or in an app, you can do a Forced Restart like this:

1. Press and quickly release Volume Up

2. Press and quickly release Volume Down

3. Press and hold the Side Button, the phone will restart. Release when you see the Apple Logo

You can find more useful information here:

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

1. Restart the device. That's it.
2. Still not solved --> Force restart iPhone - Apple Support
3. Follow the Apple article to resolve the issue --> If your iPhone, iPad, or iPod touch won't turn on or is frozen