Reply To: Limit role promotion, but maintain visibility of other roles.

[Vladimir]

You can exclude role ‘board_member’ from all user role selecting drop-down lists exactly for the user with role ‘coordinator’ using the code below:

add_filter('editable_roles', 'ure_exclude_role', 10, 1);
function ure_exclude_role( $roles ) {
    
    $user = wp_get_current_user();
    if ( empty( $user ) || empty( $user->roles ) ) {
        return $roles;
    }
    
    if ( !in_array( 'coordinator', $user->roles ) ) {
        return $roles;
    }

    // Remove board_member role from all dropdown user roles lists
    if ( isset( $roles['board_member'] ) ) {
         unset( $roles['board_member'] );
    }

    
    return $roles;
}

Also you can fully exclude roles and users with those roles from the point of view user with coordinator role with the help of “Other roles access” add-on:

Other roles access management