The only existing method I've found is using many-to-many relationships, such as by using one table for products, one table for orders, and one table where each record connects a product with an order. This is what we did for our project, and the result was not hard to work with and user unfriendly. Unless a new feature is added, we are now ultimately planning on transitioning to other platforms which can handle this elegantly, such as bubble.

A good example of what's needed here is email programs, where each email is sent to a list of recipients. Once you start typing in a name or address to add to the list you get an autocomplete box, and once you click the autocomplete option that person is added as a recipient, and there is an X by their name so they can be removed from the list as well. This sort of multi-select autocomplete would be a very welcome new option when it comes to dealing with list strings. Any option which is not an option by default would be added automatically to the list string's list of valid options.