iPhone 14 Pro Max screen brightness fluctuates despite auto-brightness and true tone being disabled

Im an Iphone 14 pro max user. I've Been having this issue from a couple of months now.

My auto brightness and true tone options are disabled but the screen brightness flickers with no apparent reason.

When I have the screen bright at max level and I'm using the phone normally, the screen bright lowers with no reason "step by step": first it goes to a 90%, then a couple of seconds or a minute later to 80% and then again to like a 70%. It restores back to normal like 5/6 minutes later. During all that time the brightness bar on the settings it's full so you can't do anything about it. This happens randomly and once or twice a day.

Is this a bug? A way to protect the device from overheating or something like that? The phone iOS is up to date. Normal use, not for gaming or "heavy duty" tasks.

[Re-Titled by Moderator]

Original Title: Screen bright lowers automatically