External SSD Formatted APFS Changes Owner Automagically

Greetings!

Setting up a new-to-me 2020 iMac refurb and because it came with a minuscule internal SSD (1/4 TB) I've stuck an external SSD (2 TB) on the back of the machine. I'm perfectly willing to boot up from the internal drive, keep my applications there, and keep my original admin account there too (if the external drive quits I want to be able to boot).

I've managed to set four accounts and move the Shared folder:

admin @ /Users/admin

user1 @ /Volumes/BigUsers/user1 pointed to by the symbolic link /Users/user1

user2 @ /Volumes/BigUsers/user2 pointed to by the symbolic link /Users/user2

user3 @ /Volumes/BigUsers/user3 pointed to by the symbolic link /Users/user3

Shared @ /Volumes/BigUsers/Shared pointed to by the symbolic link /Users/Shared

Plus I've set the Home directories for users 1, 2, and 3 so they point directly to the folders on /Volumes/BigUsers (thinking... I bet I don't need those symlinks). I did set the symlinks via the command line. [special note: I just now deleted all four symlinks and rebooted, but it didn't help]

Order of operations after setting up admin account:

1. Logged in as admin, create a user (let's use user1 for this example).
2. Log out then log in as user1.
3. User1 copies their home directory from /Users to /Volumes/BigUsers (this sets correct ownership and permissions on BigUsers/user1).
4. Log out then log in as admin.
5. Change user1's Home directory to /Volumes/BigUsers/user1.
6. Log out then log in as user1.
7. In Finder see that /Users/user1 has an ordinary folder icon, not the special one.
8. In Finder see that /Volumes/BigUser/user1 does have that special folder icon, and that owner and group is correct.
9. Delete the folder /Users/user1 and everything within it.
10. Test that user's Home directory works.
11. Repeat for the other users.

If I remember correctly, this did work. Then I added the symlinks and boom! Problem happens (or maybe it was something else, but this is what I remember, or maybe I remembered it wrong and the problem always existed (that is, I didn't look at ownership of folders I wasn't working on)).

THE PROBLEM:

/Volumes/BigUsers (the external SSD, which is formatted APFS) and all files and folders within, "automagically" take the userID and groupID of whichever user/admin happens to be logged in. Command line tools chown and chgrp don't do a **** thing--they pretend to work, but do nothing.

Extended attributes for BigUsers is "purgeable-drecs-fixed" but there are no extended attributes for user Home folders or Shared. Should I delete this? Note, it'd be pretty sweet to remove the easy drive dismount from the desktop and finder (dismount via Disk Utility or diskutil is perfectly fine).

HELP! This "automagic" behavior is pure crap. APFS should be APFS should be APFS, no matter what drive it is on. How do I fix this?

Thanks a million,

Scotty