iPhone 12 Mini Dimming and Overheating Issue

I'm experiencing severe screen dimming and overheating issues with my 12 Mini.  It occurs when, for example, the phone is charging or when I'm on a call for more than 30 min. It also occurs sporadically--for example, the brightness level was set at its maximum and the phone was locked and left untouched, but when the phone is unlocked several minutes later, the brightness level has automatically decreased. I can also share a video to demonstrate this defect. In every instance, auto-brightness and white point settings were turned off.

It not only interferes with the intended use of the product but it also raises safety concerns particularly when I'm driving and using navigation, as the screen suddenly dims, making it hard to look at directions on the phone and simultaneously focus on driving.

I visited the genius bar, but they were unable to find the cause of this problem. They confirmed that the battery and display performances are OK and the diagnostic test they ran revealed no issues. The software installed on my phone is up to date. The staff at the genius bar basically said they don't know what can be done to address this and recommended that I trade in this iPhone and get a new one. I believe this is an inherent product defect. The problem started occurring 1 1/2 years after the purchase, and there was no way I would have known that I had a defective product within the year covered by the warranty. I previously had an iPhone 6 and had no similar issues.

Has anyone run into a similar issue? What can be done to address this?