What ??? I have no idea what you are doing or trying to do.
- vboxusers group is on host
- vboxsf is inside guest
Did you remember to enable the service inside the guest?
Assuming the guest is Manjaro (at least Arch based) [root tip] [How To] VirtualBox - Installation - USB - Shared Folder
sudo systemctl enable --now vboxservice
If guest is not Manjaro - you will have to lookup how to configure that specific guest.