Due to the difference in users' information display compared to GSQL, Admin Portal doesn't allow users with admin role to a graph to create/edit/delete users or assign a user with a role to a graph. Superuser can manage users in this case. Users with Admin role to a local graph can revoke roles to other users for this local graph.
Admin Portal shows a combination of roles for proxy users. Proxy user which belongs to a proxy group inherits all the roles from the proxy group plus all the roles the proxy user has. Therefore, if you want to revoke a role from a proxy user, you need to revoke the role from the proxy group first. Then you might need to revoke the same role from the proxy user if the proxy user also has that role.
If you find any bugs, please report them to firstname.lastname@example.org. We really appreciate it!