It's not clear to me which change in 1.20.10 that upstream think solved this. The release notes are here: https://lists.x.org/archives/xorg- announce/2020-December/003067.html
Maybe this fix? https://gitlab.freedesktop.org/xorg/xserver/-/commit/c3e4c1a0fd5d4d6015e9e6317b758018317e56d1 -- You received this bug notification because you are a member of Ubuntu Desktop Bugs, which is subscribed to mutter in Ubuntu. https://bugs.launchpad.net/bugs/1896627 Title: Windows flicker when being resized with the mouse (Xorg sessions) To manage notifications about this bug go to: https://bugs.launchpad.net/gnome-shell/+bug/1896627/+subscriptions -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs