I observed the same symptoms right after upgrade to 20H2 independently on two Windows machines. On one they were mostly gone (still happen occasionally for a fraction of a second) after subsequent system updates. But on the second they persisted long time afterwards. The frequency was terrible > 1/minute and the freezing lasted long several seconds - the longer and more often the longer the system was running after boot. It was painful to do any work at all.
I was trying different things, reinstalling and upgrading divers, disabling some devices, poking with settings, changing browsers, avoiding some software - all for vain.
One day I replaced the Dynamic Desktop Theme which was shuffling beautiful images on the wallpaper with the default boring static one (single image). No more jitter, no more freezing - all gone like magic.
Hope this help some of you guys, and perhaps hint some Microsoft developers to finally reproduce the case and try to uproot the real culprit?