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?
Ok so I’ve already determined a solution for Boxes but I should mention that none what you said works for me. I’m not sure if I have a different version of Boxes than you (even though the only version that seems to exist is the one on flathub) but there is no sharing panel in settings. The only three options in settings is keyboard shortcuts, help and about boxes. When I’m running a VM, the option for “send file” is grayed out and can’t be selected.
For “devices & shares” that is, at least for me, located in the preferences for each VM. I can’t use USB devices because it’s not supported in the flatpak version and if I try to use the shared folders option, the folder I specified doesn’t show up in the VM. From what I can tell this might be an issue specific to some guests, like Windows XP, because Boxes links to a specific program that the guest needs to be running but when I try to run it in Windows XP, I get an error message stating that Windows XP isn’t a supported guest.
The only solution that seems to work for me, is taking the files I want to use in the VM and compress them into an iso file (if they’re not already) and mount it to the VM. It might be tedious but it’s the only thing that seems to be working for me.