Ive had this problem now since 2020 driver.
The screen dims and is turning it self off and on from time to time.
Ive uploaded a video of what is happening
As you can see in the video after i pull the power cable out and then push it back in the goes from dimed to normal for like 1 second then to super dimmed.
Problem is only with my HDMI monitor
Ive tried adjust the settings in radeon software but with no luck at all.
Not even a reinstalling older drivers works.
You can also follow this thread Display dimmed after boot (Adrenalin 2020)