AFAIK, there is no such thing as a "sub user" in MacOS. As Johan says, in MacOS one can have multiple users, but they are coequal. And as Johan pointed out, many of the folders underneath one user account are inaccessible to you when you are logged in under the other user account.
But I think that the fact you have two user accounts may help explain why you seemingly are running out of room. Is there a reason you have set up two separate users on your Mac Mini? Is that something that you did deliberately, or did that "just happen" as part of something that you did that had another purpose?
It would be useful to see how much space each of your user accounts are taking on your hard drive. Unfortunately, the only way to do that is to log into one of your user accounts, look at the amount of space being taken up, and then log into your other user account and look at the amount of space that is being taken up by this other user. If you try to get both pieces of information while logged in to just one of the accounts, you will get incorrect information.
As you can see, on my laptop I have two user accounts, one for me, one for my wife:
View attachment 27938
While logged in as
camner, I did a Get Info on both the
camner user folder and the
sharon user folder. These are the results:
View attachment 27939
As you can see, while logged in as
camner Finder is telling me that the
sharon user folder is only occupying 78 KB, which is absurdly wrong. The reason Finder is reporting this absurdly low, incorrect storage for amount for the
sharon user folder is that when doing a Get Info while logged in as
camner, Finder cannot see most of the subfolders in the
sharon user folder, and thus cannot calculate how much space is being taken up.
What you will need to do is to be logged in as
jeastwood75 and do Get Info on the
jeastwood75 user folder, and then log in as
jeastwood and do a Get Info on the
jeastwood user folder.
(Note that you do not need to log out from one user to login to the other user, but to be able to switch back-and-forth easily, you would need to enable "fast user switching." Since where the setting for this is differs in different versions of MacOS, go to
https://support.apple.com/guide/mac-help/switch-quickly-between-users-mchlp2439/mac and use the drop-down menu at the top to select the version of MacOS you are running and follow the directions specific to your MacOS version. Once fast user switching is enabled, you can switch users quickly from Control Center or the Menu bar if the latter is enabled.)