WooCommerce Skip Cart and Redirect to Checkout - https://njengah.com/skip-cart-and-redirect-to-checkout-woocommerce/

woocommerce_skip_cart_redirect_to_checkout_direct.php

<?php 

/**
 * Skip Cart and Redirect to Checkout 
 * Add to functions.php of child theme
 */ 

add_filter('woocommerce_add_to_cart_redirect', 'njengah_skip_cart_redirect_to_checkout_page');

function njengah_skip_cart_redirect_to_checkout_page() {
	
 global $woocommerce;
	
	// Remove the default `Added to cart` message
	wc_clear_notices();

	return $woocommerce->cart->wc_get_checkout_url();
}