I have this function and I only want to set the billing country if user is a guest, otherwise we should not change the billing country, but instead take the billing country as what the user has in his profile in WooCommerce.
add_filter( 'default_checkout_billing_country', 'bbloomer_change_default_checkout_country' );
function bbloomer_change_default_checkout_country() {
return 'US';
}