First thing to try is a different or better quality cable. Then try a different port on gpu. This could help with the flickering.
Bad freesync range (as in too wide) could be part of the issue too. Try loading a windows driver for your monitor. It has helped me with one monitor in past, but pretty low chance of helping issues.
The "artifacts on screen" is a bit worrisome though. I associate artifacts with bad memory or gpu generally, but there can be other causes.
Disable MPO
Some apps can cause issue, you might try a clean boot to see if there is an application interfering.
Disable those fancy AMD graphics options if you have any enabled and keep it simple, then gradually add them back to find the bad settings if it fixed the issue.