Only Allow 1 Product in the Cart

/**
 * @snippet       WooCommerce Max 1 Product @ Cart
 * @how-to        Get CustomizeWoo.com FREE
 * @author        Rodolfo Melogli
 * @compatible    WC 5.1
 * @donate $9     https://businessbloomer.com/bloomer-armada/
 */
  
add_filter( 'woocommerce_add_to_cart_validation', 'bbloomer_only_one_in_cart', 9999, 2 );
   
function bbloomer_only_one_in_cart( $passed, $added_product_id ) {
   wc_empty_cart();
   return $passed;
}