How do I set permissions if I don't want any group to have access?

[faeflksejfsef]

I just got a TrueNAS Mini and I'm trying to set up permissions for a dataset. I want use this dataset so my Windows machine can store its shadow copy backups there. Nobody but user "abc" needs access to this, so I set the user to "abc" in the permissions. But I'm not sure what to set the group to. I don't want to use the group "home" because then other people in home would also have access.