I’m not sure, sorry. You might be able to whip something up either with the API or Automations, but I have not investigated either one for this use case.

+1 this would be very handy to have. In general, it would be great if filters could reference the value of fields, collaborator or otherwise, and not just static strings

You actually CAN do this just by converting the join column into a Linked records field again. Airtable will automatically turn “Fred, Susan, Carrier, Barry, Larry” into five linked records. Caveat is that both the Internal Stakeholders and External ...