Hey there, in this case, i dont see the need to you to be using special list, because you want to get values from the database, in this case, movies and you can use the sort entity and get the movie id by selecting the movie on the combobox.
As you can see, I can select the movie I want to add crew now

What I did was:

Now what I am going to select is going to be saved on the variable MovieId, why? because when saving I will pass to my server action and it will know that I am adding a new person/role for that MovieId.
Don't forget that you will also need to refresh the aggregate to get the data based on the movie selected, in this case, you are going to refresh the title.
-On changing the movie, you are going to call the screen action OnChange.

- Inside of the screen action you are going to refresh the aggregate, getting the data based on the Movie(Id) selected and you are going to refresh also the title element
Let me know if I could help you.
Preview:

Kind Regards,
Márcio