We do have a feature in monday.labs that will allow you to add a board summary - this will summarise the data across all of the groups in a footer at the bottom of the board.
To add this, first select your profile picture / initials in the bottom left hand corner and then select monday.labs from the menu that appears:
You should see a blue button to active the feature (this is not shown in the screenshot as I currently have this active on my account).
You can then refresh the page, and you should be able to see a summary of the board, like so: