This gist is used in the tutorial https://www.vijayan.in/how-to-add-quantity-input-in-shop-page

quantity_render.php

add_filter('woocommerce_loop_add_to_cart_link', 'quantity_inputs_for_woocommerce_loop_add_to_cart_link', 10, 2);

function quantity_inputs_for_woocommerce_loop_add_to_cart_link($html, $product)
{

    if ($product && $product->is_type('simple') && $product->is_purchasable() && $product->is_in_stock() && !$product->is_sold_individually()) {
        woocommerce_quantity_input(array(), $product);
    }
    return $html;
}