my I phone 12 screen is black

Welcome to Apple Support Communities. We understand you need help with an iPhone stuck on the Apple logo. First, try the steps outlined in this article to form restart it:

If your iPhone is stuck on the Apple logo - Apple Support

Press and release the Volume Up button. Press and release the Volume Down button. Press and hold the Side button. Keep holding the Side button until you see the recovery mode screen.

If you still aren't able to get it powered on as expected, reach out to our support teams. You can reach them here:

Apple Support

You can also find our phone number for your region at this link:

Contact Apple for support and service - Apple Support

Take care.

Have you tried a force restart?

See this link on how to do that

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

If this steps don't work

Contact Apple Support to set up service.