Hide Menu items if the user is a Buyer

Add all the pages to the dropdown menu in admin.

After that, go to functions.php from your child theme and add the following code:

add_filter( 'wpj_as_seller_pages_filter', function( $pages ) {
    $pages[] = 17; // replace 17 with your seller page id
    $pages[] = 18; // replace 18 with your seller page id

    return $pages;
});