Hi there,
I try to use Data Tables where possible since Anvil provides a lot of built-in convenience.
In your Admin page you could try using a DataGrid component to list your content. For each row you could add an “edit” button so that you can edit a list of associated Users, and something similar to add/remove content.
In your Data Tables service, perhaps you could have a “Content” table. Your Users table could have a column that links (joins) to rows in your Content table. Any changes to the Admin page would of course update the Content table and the linked column in the Users table.
There are many ways to design such a set up. This is just what comes to mind.
For design ideas, the CRUD DataGrid and staff portal example may be helpful. I wrote a staff portal with an Admin page as well, and perhaps that might also help to generate ideas.