You can connect subitems to subitems from two different boards using this technique below and also watch video.
- In the subitems of board A, create a ‘connected boards’ column and link it to the items in board B (check two way connection).
- In board B, go to the subitems section and press add column. In the menu, press on the option “copy parent columns” and select the ‘connected board’ column (link to subitems of Board A) in board B.
This will give you the ability to connect the subitems of board B with the subitems of board A. Then, you can create mirror columns to display data from the other board.