Cumulatively count subitems that have ever been added?

We’re using subitems to track client activities, and to prevent too much bloating we’ve got an automation set up that records the subitem info to parent item updates so we can archive the subitem later.

My client wants to know if there’s a way to have a cumulative total of subitems ever created (and subsequently archived). I’m open to starting with a simple number column that gets updated through an automation or formula, but I have no idea where to start here, especially if looking for automations from the marketplace.