Thanks for your immense patience. Here’s another thing to try:
You can get almost root in the Linux VM like this (from here):
#get a privileged container with access to Docker daemon
docker run --privileged -it --rm -v /var/run/docker.sock:/var/run/docker.sock -v /usr/bin/docker:/usr/bin/docker alpine sh
#run a container with full root access to MobyLinuxVM and no seccomp profile (so you can mount stuff)
docker run --net=host --ipc=host --uts=host --pid=host -it --security-opt=seccomp=unconfined --privileged --rm -v /:/host alpine /bin/sh
#switch to host FS
chroot /host
… and then trying the mount manually:
mount -t cifs //10.0.75.1/C /C -o username=<username>,password=<password>,noperm
10.0.75.1 is the IP that the Linux guest can see your host at.