VBox | shared folder permissions

Running AlmaLinux 9.x.x as guest OS on one of my machines, using VB 7.0.x. Everything working fine…except I’m unable to give a user permission to access a shared folder. Get the 'You do not have the permissions necessary to view the contents of “sf_VBOX_share” error message.

Fine. Normally, for other OS that throw this up, all I need to do is

sudo adduser $USER vboxsf

But my attempts to do this under AlmaLinux fail miserably. Apparently, AlmaLinux requires different adduser syntax to get there from here?

Suggestions? Pointers to the obvious? Thanks in advance…