sharing files across accounts

You have to add an Access Control List (ACL) to the shared folder (and its children) to make it work as a file server.

It is best to create a folder in /Users/Shared.

chmod -R +a "group:<groupName> allow list,add_file,search,add_subdirectory,delete_child,readattr,writeattr,readextattr,writeextattr,readsecurity,file_inherit,directory_inherit" "Path/to/directory/"

You create a group in Users & Groups, then add the users to the group. Change <groupName> in the command to the name of the group you created. Change path/to/folder to the actual path to the folder, /Users/Shared/Files

Then, run the edited command in Terminal.

The change mode command sets the POSIX permissions (user/group/other) on items, and with the +a option, adds access control entries.

By default the user mask in macOS creates files with the user as owner, no group, and others (everyone) no access. The ACL overrides the POSIX permissions so others can edit files created by other group members.

Without the ACL, other users could read the files, but they would need to save a copy in order to edit the file.

You can read about it by viewing the manual page,

man chmod

You can also search the internet for Unix POSIX permissions and ACLs

Have you tried using the Shared folder in the Users folder?

You can also add folders to the Shared folder if needed.