Show Certain Products to Certain Wholesale Customers Only

add_action( 'pre_get_posts', function ( WP_Query $query ) {

    // Only affect frontend main product queries (shop, category, etc.)

    if ( is_admin() || ! $query->is_main_query() || 'product' !== $query->get( 'post_type' ) ) {

        return;

    }

    $user_id = get_current_user_id();

    // Admins / shop managers see everything

    if ( user_can( $user_id, 'manage_woocommerce' ) || user_can( $user_id, 'manage_options' ) ) {

        return;

    }

    static $default_product_ids = null;

    if ( null === $default_product_ids ) {

        // All published products

        $all_products = wc_get_products(

            array(

                'status' => 'publish',

                'limit'  => -1,

                'return' => 'ids',

            )

        );

        // Products that have the wholesale-special tag

        $special_products = wc_get_products(

            array(

                'status'       => 'publish',

                'limit'        => -1,

                'return'       => 'ids',

                'tag'          => array( 'wholesale-special' ), // tag slug

                'tag_operator' => 'IN',

            )

        );

        // Default = all products EXCEPT those tagged wholesale-special

        $default_product_ids = array_diff( $all_products, $special_products );

    }

    // Start with default products (shown to guests, regular, and most wholesale users)

    $allowed_ids = $default_product_ids;

    // Extra SKUs for specific wholesale customers

    if ( user_can( $user_id, 'wholesale_customer' ) ) {

        $extra_skus_by_user = array(

            85 => array( 'SKU4', 'SKU5' ),

            53 => array( 'SKU6', 'SKU7' ),

        );

        if ( isset( $extra_skus_by_user[ $user_id ] ) ) {

            foreach ( $extra_skus_by_user[ $user_id ] as $sku ) {

                $product_id = wc_get_product_id_by_sku( $sku );

                if ( $product_id ) {

                    $allowed_ids[] = $product_id;

                }

            }

        }

    }

    $allowed_ids = array_unique( array_filter( $allowed_ids ) );

    // Apply restriction (guests + regulars already covered by $default_product_ids)

    if ( $allowed_ids ) {

        $query->set( 'post__in', $allowed_ids );

    } else {

        $query->set( 'post__in', array( 0 ) ); // nothing visible

    }

} );