iPhone brightness dimming while watching instagram and facebook reels only

Hi I’m using and iPhone 13 Pro Max with latest iOS and I’ve been experiencing a dimming effect only on meta apps - instagram and FB only while viewing reels only not stories I’ve googled the issue and many have it without any resolution I’ve tried removing below with no effect

-HDR from app -Attention aware feature -Auto brightness -True Tone -Night shift

And still the iPhone dimes watching meta reels only

All other apps doesn’t do that at all only meta reels

I’ve reinstalled instagram and fb and still same and reset iPhone with newest iOS still same

Note: phone is cold using at home even when i used it first thing in morning or anytime durying day.

Kindly advice

Thanks