virtualbox.org

Same problem with my Windows 10 20H2 guest.

I hadn't used my VB-VM for a long time, so I had multiple updates running. After installing Windows update 20H2, I experienced severe input latencies in the Windows search input and could no more shut down via mouse clicks, because only parts of the menu were visible but did not respond.

Switching off 3D acceleration turned out as a workaround...

Klaus.Kraemer wrote:After installing Windows update 20H2, I experienced severe input latencies

This can be expected. Windows needs a day of running in a VM to settle and index itself post-installation.

Klaus.Kraemer wrote:only parts of the menu were visible but did not respond.

Also known, when 3D is enabled. Disabling Settings > Personalization > Colors > Transparency Effects fixes this. Disabling 3D also is a work-around but may leave the VM running slower too.