SOLVED - iPhone 12 Max Pro Dimming.
A non-apple case causes it to overheat!
My iPhone was fine for two years and I switched from the Apple purchased case that I bought at the Apple Store for a non-Apple case to enjoy a new color. Didn’t think about it but started having problems with my phone dimming.
It was constant if I was googling or reading texts etc it would toggle up and toggle down from bright to dim so I could barely read it. It was ridiculous.
Tried everything the Internet suggested. Turning it off helped but that was only because it was cooling it off. It didn’t solve it. Changing any and all settings did absolutely nothing.
Read a post that mentioned they thought it was an overheating issue. Remembered that I had just purchased a new case before this started. Put back on my Apple purchased case. Voila. No issue for a whole month. SOLVED