It's an Odyssey G7, less than a year old. But I am not sure what the issue can be. The entire system is less than 1 year old. GPU is a EVGA 3080 ULTRA FTW3, using DP cable from GPU to monitor.
What was weird is that when it turns darker, it seems to do it only during browsing or something, never noticed it in a game. And when I wanted to take a print screen to be able to show you know.. "This is Pic 1 when it darkens, this is Pic 2 during normal times" they were both the same, so print screen did not recognise the shift.
It's a pretty well, minor issue that arises rarely, just not sure what it could be.