Yes, this topic comes up a lot, but generally it has to do with ACF fields. The issue is that ACF uses the standard WP search to find posts, meaning it only searches title and content. In order to include something else you need to modify the search query to include what you want to add. Here is a link that explains doing this https://adambalee.com/search-wordpress-by-custom-fields-without-a-plugin/
In order to add this to ACF what you need to do is to create an acf/fields/relationship/query filter. In this filter you would add the other filters that will make the changes to the query.
