"What causes iPhone 12 screen damage and can I repair it?"
-------
Thank you for the photo.
I agree 100% with Lawrence about it not being worth the cost. So, take this as a good reason to get a new iPhone.
Applying a Liquid Fix:
Looks like big crack to me. So, when it comes to smartphones, if you don't have AppleCare on your iPhone, then one thing to consider is using a liquid fix called Liquid Nano or Liquid Armor. Retailers sell it, and some even apply it to the iPhone for an additional cost. As for a protector case to use, I recommend an OtterBox. Note: Placing liquid fixes to the iPhone's screen (i.e. Liquid Nano or Liquid Armor) would cancel your AppleCare coverage. So, avoid applying any liquid fix, whatsoever, if you have AppleCare on your iPhone.
Transferring to a New iPhone:
If nothing is enabled in iCloud (i.e. Contact snapshot Photos), and important info is on this, then you might need to get the screen replaced, in oder to successfully transfer info to your new iPhone.
Two Methods - Quick Start or iCloud:
Use Quick Start:
The transfer may have stalled. So, is Quick Start what you used here? Either way, I recommend you restore your new iPhone to factory settings, and then perform this once more, using Quick Start: Use Quick Start to transfer data to a new iPhone or iPad - Apple Support
Sync Through iCloud:
Sign in to the same iCud Account on both devices. Then enable items (i.e. Photos) in iCloud on both phone. All pertaining items will be accessible between the two devices. As an example, here is how to go about this for Contacts:
On Both iPhones...
- Go to: Settings
- Tap: Your Name (Top Item)
- Tap: iCloud
- Tap: Contacts
- Enable: iCloud Contacts