IPhone X brightness won't go higher than 80 percent?

My IPhone X randomly dims to about 80 percent brightness and sliding the brightness dimmer only adjusts the brightness up to 80percent max, sliding it farther causes no change and sliding it to 90percent or 100percent still looks the same as 80percent. If I wait long enough my screen will randomly get brighter again and go to 100percent on its own. Then later, my phone will randomly dim again to about 80percent again. I checked auto brightness, I checked white point and I even checked low power mode but none of that fixes the issue. I just have to wait until my iPhone decides to randomly fix itself and goes back to full brightness again.

Hm

May be a hardware related problem. Try this 1. Go to Settings 2. Tap on General 3. Tap on Reset at the bottom 4. Tap on Reset All Settings then Reset All Settings again to confirm---This lot times can fix issues with brightness and connection and app issues and such

That happens when the phone is under load & heats up enough. Normal.