bitfenix

Forgot to write so we can mark the topic as solved :>

If someone need the same thing, the solution was:

add_filter('bring_shipping_rates', function( $rates ) {
	$shipping_classes = [
		'freeshipping',
	];

    $free = false;
	$items = WC()->cart->get_cart();
	foreach ( $items as $item ) {
		$shipping_class = $item['data']->get_shipping_class();
		if ( in_array( $shipping_class, $shipping_classes ) ) {
			$free = true;
		}
	}

    if ($free) {
        $rates[0]['cost'] = 0;
    }
	return $rates;
}, 999 );

This code is placed in theme’s function.php file. Before this, shipping class needs to be created (name of the shipping class will be matched here https://prntscr.com/qgv9wf)

After that these lines are commented https://prntscr.com/qgvd6w in the wp-cart-functions.php in the woocommerce plugin

I knew I should be a backend dev : ) Thank you for providing example code, will place it in child theme function file and then try to modify it.