Thanks for your patience. As mentioned by @john, Adobe After Effects has released a patch update which provide a fix for the preview issues on 16" MacBook Pro. For more information, please check https://helpx.adobe.com/after-effects/kb/fixed-issues.html
Same here. seems to be an incompatibility with some of the new cards. I was on the phone with adobe for an hour the day i got this machine, the verdictfrom the tech on the call was: 'use AE2019 for now, call AMD about updated drivers'. !!
Try changing the Video Rendering and Effects from Mercury GPU Acceleration (Metal) to Mercury Software Only from the Project Settings. Project settings can be accessed from the File menu.
Also, check the System Compatibility Report under the Help menu.
Vishu AggarwalAdobe Certified Instructor, Professional and Expert
That's the first thing I tried. Nothing changed. Rolled back to CC2019 on both Premiere and AE, and just accepted that Adobe release beta versions now (but still charge you the full whack).