iPhone 12 Pro Max Dimming without auto brightness

I bought my iPhone 12 Pro Max a few weeks ago, and recently I’ve noticed that my brightness level dims significantly. I’ve checked other forums and discussions but none of the solutions have solved the issue for me. Auto brightness is off, True Tone is off, Zoom > Low light is off, iPhone isn’t charging, iPhone isn’t low on battery, I’ve reset settings, soft rest device, and I’m also indoors with air conditioning and my phone is room temperature. I noticed it started dimming at 50% every 30 mins. I would increase the brightness and then would set down my phone on my desk without touching it and 30 mins later, it would be dimmed at 50%. Today I noticed it’s dimming to the lowest setting possible. It’s happened 4 times since 8:30am (and it is currently 10:45am). I’ll put it to max brightness and then a few minutes later, it’ll be completely dimmed again. Not sure how to fix this. Has anyone else had this issue and how did they fix it?