Override loop template and show quantities next to add to cart buttons

Add this code to your child theme’s functions.php file or via a plugin that allows custom functions to be added, such as the Code Snippets plugin. Avoid adding custom code directly to your parent theme’s functions.php file, as this will be wiped entirely when you update the theme.

if ( ! function_exists( 'YOUR_PREFIX_quantity_inputs_for_woocommerce_loop_add_to_cart_link' ) ) {
  /**
   * Override loop template and show quantities next to add to cart buttons
   * @param  string $html    Default loop template.
   * @param  object $product Product data.
   * @return string          Modified loop template.
   */
    function YOUR_PREFIX_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() ) {
            $html  = '<form action="' . esc_url( $product->add_to_cart_url() ) . '" class="cart" method="post" enctype="multipart/form-data">';
            $html .= woocommerce_quantity_input( array(), $product, false );
            $html .= '<button type="submit" class="button alt">' . esc_html( $product->add_to_cart_text() ) . '</button>';
            $html .= '</form>';
        }

        return $html;
    }
    add_filter( 'woocommerce_loop_add_to_cart_link', 'YOUR_PREFIX_quantity_inputs_for_woocommerce_loop_add_to_cart_link', 10, 2 );
}