iPhone 16 pro max screen frozen

Try a forced restart. Please follow the step by step instructions in the Apple Support article I linked to below. If that doesn’t resolve the issue, you need to have Apple perform diagnostics on your iPhone. It can be done in person at an Apple Retail Store or at an Apple Authorized Service Provider. You can also contact Apple Support and request remote diagnostics.

If you’re in the US, please call  1-800-MY-APPLE, or outside the US, consult the support articles below. In Canada, call 1-800-263-3394.

Contact Apple for support and service - Apple Support

Genius Bar Reservation and Apple Support Options - Apple

Explore Service Locations

Official Apple Support

You need to have Apple perform diagnostics on your iPhone. It can be done in person at an Apple Retail Store or at an Apple Authorized Service Provider. You can also contact Apple Support and request remote diagnostics.

If you’re in the US, please call  1-800-MY-APPLE, or outside the US, consult the support articles below. In Canada, call 1-800-263-3394.

Contact Apple for support and service - Apple Support

Genius Bar Reservation and Apple Support Options - Apple

Explore Service Locations

Official Apple Support

For the remote diagnostics you would need to set it up by contacting Apple support in one of the links posted by Jeff Donald. Click on Apple Support Options or Official Apple Support.

Here is the link to force restart:

Force restart iPhone - Apple Support

Forgot to add that link, sorry! However, FelipeV has provided the same link I intended to.