Windows runs great with 1709 version, but is extremely slow with 20H2 update. What seems to be the problem? Windows becomes so slow that I literally have to wait minutes to do simple tasks like opening up a browser, or file explorer, or even simply right click on the desktop.

In the task manager, it shows 100% disk usage, and the services that are mostly at play here are "system, "antimalware service executable".

I can't even tell what the issue really is. I was thinking it may be because of of my HDD, since I don't have any SSD in my system. But windows works fine with previous build versions.