I have a Ubuntu OS running inside a VM made on Virtualbox.
It's some time that I cannot see anymore the content of my shared folder from my Ubuntu OS. I am loading content into the shared folder form the external OS: windows10.
I have configured the shered folder from virutalbox UI like so

The UI tells me as I try to access the sf_VirtualBox_cartella_condivisa_VM03
:
"you do not have the permission to view the content of..."
which I understand, because Isee a red cross icon over the folder icon.

Then I have run
tommaso@tommaso-VM3:/media$ sudo adduser $USER vboxsf
[sudo] password for tommaso:
but I get
The user `tommaso' is already a member of `vboxsf'.
I restarted the vm but the problem remains.
Inspecting the content of folder media, I get
tommaso@tommaso-VM3:/media$ ll
total 16
drwxr-xr-x 4 root root 4096 lug 31 14:56 ./
drwxr-xr-x 20 root root 4096 lug 31 14:48 ../
drwx------ 2 root root 4096 lug 31 14:56 sf_VirtualBox_cartella_condivisa_VM03/
drwxr-x---+ 3 root root 4096 nov 8 15:06 tommaso/
So I have opened have opened another VM having the shared folder working, and I see that the permissions and user are different
tommaso@tommaso-VirtualBox:/media$ ll
total 24
drwxr-xr-x 4 root root 4096 giu 24 2021 ./
drwxr-xr-x 20 root root 4096 ago 2 2021 ../
drwxrwx--- 1 root vboxsf 12288 nov 1 10:58 sf_VirtualBox_cartella_condivisa/
drwxr-x---+ 4 root root 4096 nov 8 15:24 tommaso/
So I have tryed to "align" them manually by running:
sudo chown root:vboxsf /media/sf_VirtualBox_cartella_condivisa_VM03/
sudo chmod g+rwx /media/sf_VirtualBox_cartella_condivisa_VM03/
so that I get
tommaso@tommaso-VirtualBox:/media$ ll
total 24
drwxr-xr-x 4 root root 4096 giu 24 2021 ./
drwxr-xr-x 20 root root 4096 ago 2 2021 ../
drwxrwx--- 1 root vboxsf 12288 nov 1 10:58 sf_VirtualBox_cartella_condivisa/
drwxr-x---+ 4 root root 4096 nov 8 15:24 tommaso/
restarted the VM but the problem remains.
And if I try to access the shared folder form my explorer folder UI I get
authentication is required to access gvfsd daemon

What could I possibly did wrong? How can I fix it?