How to Auto-generate a Title based on a multiple entries titles? (using a Entries field type)
Not sure if this can be done in the shorthand syntax, but you can do this using Twig for the dynamic title format. The key is to use map to turn an array of entries into an array of titles and then join them. Something like this should work:
{{ object.movies.all()|map(movie =&gt; movie.title)|join(', ')|default('No movies selected') }}

Also note the default filter, which is a nice fallback in case no entries are selected in your movie field.