Is it possible to query some sub collections from a list of document references ?

Good evening everyone,

I would like to perform a Backend Query on the "workoutClient" subcollection of certain clients. However, Flutterflow only offers “all sub-collections” or “a sub-collection of a single client (the from variable)”. I have a document reference list of users and I would like to call only those. Do you have a technique? THANKS !