Filter free shipping by category on woocommerce

I would even use this plugin, but it’s such a basic thing, that it doesn’t need a plugin (at least I think)

I tried the following code in php functions, but it does the reverse, it only shows free shipping, how would I do to do what I want?

add_filter( 'woocommerce_package_rates', 'custom_shipping_methods', 100, 2 );
function custom_shipping_methods( $rates, $package ){

    // Define/replace here your correct category slug (!)
    $cat_slug = 'my_category_slug';
    $prod_cat = false;

    // Going through each item in cart to see if there is anyone of your category
    foreach ( WC()->cart->get_cart() as $values ) {
        $product = $values['data'];

        // compatibility with WC +3
        $product_id = method_exists( $product, 'get_id' ) ? $product->get_id() : $product->id;

        if ( has_term( $cat_slug, 'product_cat', $product_id ) )
            $prod_cat = true;
    }

    $rates_arr = array();

    if ( $prod_cat ) {
        foreach($rates as $rate_id => $rate) { // <== There was a mistake here
            if ('local_pickup' === $rate->method_id) {
                $rates_arr[ $rate_id ] = $rate;
            }
        }
    }
    return !empty( $rates_arr ) ? $rates_arr : $rates;
}