Working with lists is done differently depending on the list type.
For example, if the type is String, you can add entries by typing strings in the String field of the Add String window. However, if the type is MediaType, you need to select an entry from a media type folder, which is part of a system of folders.
For string and wildcard expression lists, there is the option to add multiple entries at once by clicking Add multiple and typing text for each entry in a new line.
For media type lists, you can select multiple entries or folders at once if you do not want to add them separately.