WooCommerce: Sync Product Quantities @ Cart

/**
 * @snippet       Sync Cart Item Quantities
 * @how-to        Get tutoraspire.com FREE
 * @author        Tutor Aspire
 * @compatible    WooCommerce 4.0
 * @donate $9     https://tutoraspire.com
 */
   
add_action( 'template_redirect', 'tutoraspire_sync_cart_quantities' );
   
function tutoraspire_sync_cart_quantities() {
    if ( WC()->cart->is_empty() ) return;
$master_product_id = 20;
$in_cart = false;
foreach( WC()->cart->get_cart() as $cart_item_key => $cart_item ) {
if ( $master_product_id === $cart_item['product_id'] ) {
$qty = $cart_item['quantity'];
$in_cart = true;
break;
}
}
if ( ! $in_cart ) return;
foreach( WC()->cart->get_cart() as $cart_item_key => $cart_item ) {
if ( $master_product_id !== $cart_item['product_id'] ) {
WC()->cart->set_quantity( $cart_item_key, $qty );
}
}     
}