It's a long shot, but miracles happen so here goes:

The goal of my automation is to create a 'Done' activity on the relevant deal in Pipedrive whenever we send an auto-message through a campaign in Intercom.

For what I want, there's no direct integration from Intercom to Zapier so I'm looking at their webhooks instead (to parse to Zapier as trigger). The only webhooks they have available however seem to be based on conversations, not messages (Intercom users will know the difference).

Has anybody found a solution?

Here's a list of their topics you can subscribe to for notifications: https://developers.intercom.com/building-apps/docs/webhook-model#section-webhook-topics

Really hope someone bumped into this issue too and has found a solution for it in the past! I know it's more a question for Intercom user groups but I couldn't find any active ones. Who knows, maybe a fellow Pipedriver knows the answer :)