iPhone keeps randomly turning off

This is probably the best answer. I took the sim out before seeing this post, but had to take the phone (13 mini) to the Apple Store since I was at a point where it wouldn’t charge, and it wouldn’t even get to the unlock screen before shutting down again. I noticed that the SIM card was actually the problem and removing it earlier when I still had the ability to reset while it was attempting to charge would have most likely fixed the phone and prevented it from getting damaged more to the point where it doesn’t finish booting at all. When I took it to Apple they said it was a rear harness issue since the phone wouldn’t charge at all it wasn’t a battery issue. They obviously recommended I replace the entire part $299 or buy a replacement 13 mini for $400. Apple has seriously gone down hill and they’ve become more like an auto dealership that doesn’t fix the problem or repair decides, but just recommends the most expensive and profitable option (replace the majority of the components, or buy a new phone). I’m sure Apple is aware that the SIM cards are causing the logic board/rear assembly to become unusable, but knowing Apple it’s either a known planned obsolescence method, or they are award of it and prefer to let the phones die from their software update/sim malfunction to make people buy new phones and hardware for repair.

I can confirm that the SIM card was the main issue, since after I removed the sim and tried to use a back up work phone (iPhone 8) until I got a replacement, the phone did the exact same thing as the 13 mini started to break which was go from around 30% battery down to 1% and say it was charging initially but unable to go above 1%, then eventually not say charging at all and continue rebooting. Once I took out the SIM card after noticing that the exact same thing was happening to my iPhone 8, the battery went right back to its previous charge of 30% without it having charged back up. It was then able to charge normally and stopped power cycling. Something with the iOS update causes the sim to overload the logic boards ability to charge the battery, and that inability to charge will cause the phone to be unable to have enough battery to finish booting. Apple knows this is the issue since another used mentioned that an Apple Genius had recommended removing the sim and resetting to fix the problem, but they keep these solutions from the rest of the company/sales people/technicians or tell their employees not to mention it to their customers so the phone will become unusable/unrepairable with this method and they can try to profit from replacing huge components or forcing users to buy a new phone which is all they care about.