The black level on decoded content is incorrect (Limited vs Full). It becomes very obvious if you watch something with baked in black bars. (The two black bars should be the same, but the black bars in the video is grey [value 16] and the actual black bars are black.)
I have been having the same problem on all AMD Drivers past 20.4.2. I updated once previously but rolled back, now I require the update for Horizon Zero Dawn.
Anything using Playready (Microsoft) DRM (Netflix on Edge/App, Amazon on Edge) suffer, when playing resolutions above 480p.
Widevine (Chrome, Firefox) is not effected, but limits Netflix to 720p.
Both my monitors support HDCP for 1080p content, and work perfectly on 20.4.2 and before.
Win 10 2004 3700x RX480 Driver 20.8.1
Thanks for the share, if it bothers you then return to a driver you were happy with. Make sure to run DDU before regressing a driver for a clean slate.
Do report your issue to AMD support: https://www.amd.com/en/support/contact-email-form