Iphone 12 won’t open totally.

• Restart the device. That's it.
• Still not solved --> Force restart iPhone - Apple Support

• Follow the Apple article to resolve the issue --> If your iPhone, iPad, or iPod touch won't turn on or is frozen ...

(1) Try and Force Restart your iPhone EXACTLY as shown below and see whether that resolves the issue:

• Press and quickly release Volume UP button
• Press and quickly release Volume DOWN button
• Press and Hold the SIDE button until an Apple logo appears and then release the Side button (Can take up to 20 seconds. (DO NOT release Side Button when invited to Slide Power OFF). 

(2)  If the above does not work then - Follow the instructions in this article by Apple ➔ If your iPhone is Non-Responsive or Frozen and see if that helps.

(3)  If that does not help your phone might need service ➔  Contact Apple for support and service - Apple Support

Axel F.

Please follow the steps in the following link for support with this issue: If your iOS device restarts or displays the Apple logo or a spinning gear unexpectedly