The Searchanise extension doesn't index products with Visibility = Not Visible Individually or Catalog. So you can set up one of these values in the product Visibility in the Magento admin panel to hide products from search.

To change Visibility for a product to hide it from the search, follow these steps:

  1. Go to the Magento admin panel > Catalog > Products.
  2. Click the product to edit it.
  3. Select a Not Visible Individually or Catalog value in the Visibility field. 
  4. Save changes.

That's all. You can go to your storefront and make sure that the product doesn't appear in the search results.