I run a Windows 10 Host for VirtualBox and the Guest is Ubuntu.
An awful lot of people have been having a problem over the years where they can’t mount the shared folder from Windows to Ubuntu because of the wrong fs type error, even after installing the VirtualBox Guest Additions
You can only connect to a Windows 10 share by having the VirtualBox Guest Utils installed as well and this is the command that installs it.
sudo apt-get install virtualbox-guest-utils
Now you can mount the shared drive.