How to open another Account's User folder using Terminal?

When you use the login command, you're switching accounts. You cannot then open the file in your current Finder/account if your current account doesn't have access.

The analogous operation to doing login when interacting with Finder would be to fully switch over to that account. All running GUI programs are going to be using your current account.

If you frequently need to access these files, you could keep them in /Users/Shared or you can change the permissions on them (if you select the folder the files are in you can make that folder accessible to both accounts and recursively apply it to contents).

Jump Desktop will allow you to log in to the same computer you are using as a different user. You will have access to all of your files and apps.

I have not done this extensively, but I did test it and it worked in Jump Desktop.

The default macOS Screen Sharing.app will not do this.

Screens 4 seemed like it was going to work, but it did not successfully connect.