We need a multi-board mirror connection from an item (main board) through a single column to subitems from multiple different boards.
We know that multi-board mirror connections are supported at the item level across different boards. However, this is not available for subitems. To connect subitems to items, the mirror must be created from the subitem level, and once it is set up, it is not possible to add subitems from another board at the item level.
What are you trying to achieve
We want to connect a single item on a main board to subitems from multiple different boards using one mirror/relation column, and mirror their data in one place.
You’re right - this is presently not supported by monday.
You can try the Mirror Item Multiple Boards app. It allows you to add the same item with subitems on multiple boards with full live syncing(updates + replies).
So you can also use regular columns instead of mirror columns. It also will allow you to setup automations on them.
You could create a master board with tasks from different board.