Multiselect element + database query

Has anyone implemented WeWeb’s out of the box multiselect element so that it dynamically searches the database, rather than selecting from a simple array for the dropdown?

I have a large collection of locations, that I can’t preload, or else my website will crash. I am having trouble triggering the database search when a user types a search option in the multiselect. Neither “On change” nor “On init change” work as a trigger.