In a web map I use a count on the object id from a Relationship class in Configure Attributes like this.

This is handy for telling me how many related records exist in the pop up like Forms Found: {relationships/4/objectid}
This is not working in the new or old Collector however. I understand that Arcade cannot do FeatureSetByName and such offline but I would think if the related records are on the device this Count should work.
Ideas?
Thanks