To show all of the clickable links, author does need to be a list:
So you took the right step in changing the type to list. (Remember to have a backup before mass editing anything.)
If you then got a warning (that you weren’t getting before) about expecting text, that sounds like your base has a filter related to author that relies on text.
You could share your filters here for help identifying which one(s), or just remove all filters that have to do with author. After you’ve changed author to a list, you could use the Simple filter builder to re-add them; that way you’ll have a better chance of building a filter for the right type.