WooCommerce Disable guest checkout for certain products

functions.php

<?php

// Code goes in theme functions.php or a custom plugin
add_filter( 'pre_option_woocommerce_enable_guest_checkout', 'conditional_guest_checkout_based_on_product' );

function conditional_guest_checkout_based_on_product( $value ) {
  $restrict_ids = array( 1, 2, 3 ); // Replace with product ids which cannot use guest checkout
  
  if ( WC()->cart ) {
    $cart = WC()->cart->get_cart();
    foreach ( $cart as $item ) {
      if ( in_array( $item['product_id'], $restrict_ids ) ) {
        $value = "no";
        break;
      }
    }
  }
  
  return $value;
}

6 years old and still works for me. Thank you!