It appears QBs is requiring sign in to your online account after logging into the local company file. After doing this the "services" (drag and drop) are restored. I was having the same problem and did all of the above with no effect. QBs tool reported no issues also. I was still able to attach files manually but only the drag and drop function was removed.  On 11/29/2020 it worked and then on 11/30/2020 drag and drop stopped working.