iPhone 12 Pro Max dimming

My phone is dimming the display automatically despite having disabled this in both settings> display and brightness and settings> Accessibility > display and text size. I’m running the latest iOS. The only trend with this issue I can identify is that the device gets rather warm prior to the display dimming. Not always but often. This happens during regular out and about use, not when it’s plugged into charge or sitting on a Qi or something. Could very well not be connected but given strangeness of the dimming despite being twice disabled I thought it may be worth mentioning. Any advice?