Signal/Cellular data loss on iPhone 12 Pro Max.

Hey there,

If you try all these steps and still have this issue it could be a hardware issue, however take a look at these articles:

See ☞ If you see No Service or Searching on your iPhone or iPad - Apple Support

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See ☞ If you see a Cellular, Ultra Wideband, or Apple Pay Issue message after an iOS update or restart - Apple Support

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See ☞ If you see 'invalid SIM' or 'no SIM' on your iPhone or iPad - Apple Support

if all of that doesn’t work for you , Your next step will be to go to one of Apple's centers or Apple Authorized Service provider you can find one by this link ☞ Apple - Find Locations

I had the same problem and tried everything. Ended up taking it to Apple and it was diagnosed as a failure on the SIM card connector, basically a $600 repair. The technician said he had never seen this failure before and was surprised as my phone was in great shape. So after one and a half years of use my phone was garbage. Even more frustrating was that it was worth $0 on trade for a new phone. I was really expecting better service given the age and condition of the phone.

If that's the case, it seems to me like I'm willing to at least attempt a  Taptic Engine Bundle & RF Cowling replacement myself with the new Self Service Repair Apple is offering. LOL! Way less than $600, and if it possibly saves the phone, then it's a win! If not, i'm out less than $100.

Apple - Support - Manuals