Install live linux on your VirtualBox and it should be enough, they are rather small for that very reason. There are plenty of them to choose, (here is small list with desriptions). I personally use slax on usb but there are others. Nothing prevents you from making your own live version that would be absolutely minimalistic after you get comfy with ready ...
Please try adding vers=1.0 to the mount options. If that still fails then replace 1.0 with 2.0, 2.1, 3.0 in turn. Keep the highest value that works.
What you're doing here is downgrading the SMB version from the current (3.1) to the oldest (1.0). Many older devices still only use SMB version 1.0.
For me on Fedora Rawhide 33 I needed to use one the following in "/etc/samba/smb.conf":
client min protocol = CORE
client min protocol = NT1
and define the host in "/etc/hosts":