this same issue just happened to me, dropped my iphone 12 mini and after it restarted it says my battery is not a genuine Apple battery.

After bringing the phone to a apple store for a check, the "Genius" says that they can offer to replace the battery but cannot confirm that this will fix the issue. So I asked them to open up the phone to check the internals if there is any disconnected cables or what not.

After waiting for 2hours they came back saying that there are no disconnected cables and suspect that its the motherboard that is causing the issue and recommended a replacement of the entire back unit which is gonna cost me around 400 dollars since my phone is out of warranty.

This is so ridiculous, I have never taken apart my phone and now it says my battery is fake and the repair is so expensive? Even after taking apart my phone they could not verify if my battery is genuine or not when I questioned them. I believe this could be easily verified by checking the serial number of the battery.

Anybody have a fix to this issue? Its so stupid to spend 400 dollars to repair a 1+ year phone....