Symptom:
When you try to disable it, you can't save changes because the OK button isn't usable. you can't run the VM's if it's enabled.
Solution:
Virtualbox 6.1.x requires the computer to have "virtualization technology", VT-x or AMD-V or SVM. If your computer doesn't have this, then you can only run 6.0.x or earlier.
Source: Virtualbox.org
