Hi @Rios,
For use Multiselect drop-down component you can have a many to many relationship and before you come to that screen you need to create the record and in that screen you can update it!
Check this : Multi-Select Dropdown issue (only last item selected works) - #3 by dilon_perera
This video is about using Logged in user to filter the list.
You can create a many to many relationship on the collection that you are trying to create the record with the dropdown values and then before you come to this screen you can add a Create action on that collection and then you can add the link action to go to that screen and in that screen in the multiselect drop-down component you can add the Update current record and add current value of the multiselect drop-down to the that many to many relationship property!
Thank you