There are some gigabytes of system updates and app updates since the release of Nokia 6, with various fixes and improvements.
Using a reliable WiFi, please confirm that the phone is fully updated?
The screen should not flicker visibly. Some chargers are more noisy than others, and some eyes are more sensitive to flicker than others.
FWIW, I'm sensitive to less than 80Hz and my Nokia 6 does not flicker with the screen at maximum brightness and the wall charger attached.
If you are still unhappy with the phone screen performance after updating, then I suggest you consult the place of purchase or a technician for proper evaluation.
my phone is up to date and I don't think so my eyes are sensitive waiting for oreo may be this is a software glitich don't know much about harware issue