My new iPhone is stuck in settings

Try a forced restart https://support.apple.com/guide/iphone/force-restart-iphone-iph8903c3ee6/ios

If that fails and if this is indeed a brand new phone then take it back under warranty or use your free apple technical support

Depending on your region, you may be able to reach them here: Get Support

If this is a new-to-you but pre-owned phone then see the process below. Work all through it.

If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support

There is no guarantee you can save any data since your last backup

If it fails more than 3 times seek a refund.

if you can force restart it so you get back to a home screen you can usually ignore the Finish setting up part for a while.

If you have a brand new iPhone 12 then use your free tech support using the Get Support link I gave earlier.