Try:

var rooms = await FirebaseFirestore.instance
  .collection("rooms")
  .where("users", arrayContains: userId)
  .orderBy("latestMessageTime", descending: true)
  .snapshots();

I have a Stream which seems to work perfectly fine: Every print statement you see in the stream is getting printed. Also when calling if(snapshot.hasData) it apparently is true. But still, my stream only returns the following: AsyncSnapshot<List<dynamic>>(ConnectionState.done, [], null, null).

What do I need to change in order to be able to access the Data in my retVal variable?

   Stream<List>? roomsListStream() {
    try {
      List<RoomsListModel> retVal = [];
      print("userId: $userId");
      var rooms = FirebaseFirestore.instance
          .collection("rooms")
          .where("users", arrayContains: userId)
          .orderBy("latestMessageTime", descending: true)
          .snapshots();
      print("rooms: $rooms");
      rooms.forEach((element) {
        element.docs.forEach((element) {
          print("element: $element");
          var room = element.data();
          print("room: $room");
          var roomId = room["roomId"];
          var otherUserId =
              room["users"].firstWhere((element) => element != userId);
          var lastMessage = room["latestMessage"];
          var lastMessageTime = room["latestMessageTime"];
          print("otherUserId: $otherUserId");
          getOtherUser(otherUserId).then((value) {
            print("value: $value");
            var avatar = value["photoUrl"];
            var name = value["name"];
            retVal.add(RoomsListModel(
                roomId: roomId,
                otherUserId: otherUserId,
                avatar: avatar,
                name: name,
                lastMessage: lastMessage,
                lastMessageTime: lastMessageTime));
          });
        });
      });
      return Stream.value(retVal);
    } catch (e) {
      print("Error: $e");
    }
  }