WooCommerce - Add a Buy button, when it's clicked the product will be added to your cart (as Add to Cart button) but you will be redirected to checkout page

functions.php

<?php
// Add buy button on content-product listed in archive-product
function k_woocommerce_loop_add_to_cart_link($element, $product) {
  
  // With variable products you have to select options
  // You cannot redirect the user without having the options selected
	if($product->product_type != 'variable' && $product->is_in_stock()) {
		$element .= sprintf( '<a href="%s&buy=1" rel="nofollow" data-product_id="%s" data-product_sku="%s" data-quantity="%s" class="button %s product_type_%s">%s</a>',
			esc_url( $product->add_to_cart_url() ), // it adds 'buy=1' in parameters of URI
			esc_attr( $product->id ),
			esc_attr( $product->get_sku() ),
			esc_attr( isset( $quantity ) ? $quantity : 1 ),
			$product->is_purchasable() && $product->is_in_stock() ? 'buy_button' : '', // class
			esc_attr( $product->product_type ),
			esc_html('Comprar')
		);
		
	}

	return $element;
}

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

// Redirect after buying clicking in Buy Button added above
function k_add_to_cart_redirect($url) {
	if ( ! isset( $_REQUEST['add-to-cart'] ) || ! is_numeric( $_REQUEST['add-to-cart'] ) ) {
		return $url;
	}

  // Your buy button add 'buy' parameter in URI, so you can know when you have to redirect the customer.
	if(isset($_REQUEST['buy'])) {
		return WC()->cart->get_cart_url();
	}

	return $url;
}

add_filter('woocommerce_add_to_cart_redirect', 'k_add_to_cart_redirect');