I tried looking into this myself but I couldn’t really find much about this error. The only solutions I could find didn’t work for me. The first one was to use mokutil but at the point where I was supposed to run sudo mokutil --import MOK.der it gives me the error message “Failed to get file status, MOK.der” even though I did everything it told me to do. The other one was to disable secure boot and then run sudo '/sbin/vboxconfig' but even though it looked like it worked, I’m still getting the error message. I have re-enabled secure boot, so you don’t have to worry about that.
Is there something else I can try or does VirtualBox not work in Linux Mint for some reason?
6.1 is the newest version included in your OS. That’s just how Linux works.
Downloading newer versions from somewhere else is sometimes possible, but can lead to a lot of headaches, especially with packages that interact with the kernel.
If you notice you keep running into this issue and using the newest stuff is important to you, consider switching to OpenSUSE Tumbleweed. It’s the most beginner-friendly rolling release distro.