“Nested VT-x/AMD-V" can not be changed by default
On [Processor] page of the Virtual Box 6.x, “Enable Nested VT-x/AMD-V" is grayed out and cannot be changed.
Solution : Execute a VBoxManage command
Move to the directory where Virtual Box is installed on. Then execute the following VBoxManage command.
VBoxManage modifyvm <Your Vbox name> --nested-hw-virt on
Result: “Enable Nested VT-x/AMD-V" is turned on.