iPhone 12 mini screen dims very dark when plugged into charger

I updated to the latest version, that didn’t solve the problem, however I believe I have found the solution. The problem was occurring because the phone was overheating. The screen would dim and the flashlight would stop working as well. I was using an off brand charger from a discount store. I picked up the mophie 18w usb c car adaptor from the Apple store in Nashville. Now that I am charging the phone with a mfi certified charger I am having no problems. Thanks!

version is 14.4.2. True Tone is enabled. I’ve tried turning on/off the auto brightness feature. I have tried turning True Tone on/off. The brightness meter is all the way up. It really only occurs after plugging in the charger. When it dims the brightness meter is all the way up but if you move it all the way down and then back up you’ll notice the brightness stops getting brighter at the half way point of the meter. Everything after the half way part of the meter, the brightness just stays the same. The problem goes away a out after 5 mins of using the phone unplugged. I’m starting to think it may be a defect.