Short answer
HubSpot's KB on workflow object types gives the example: create a deal record anytime a demo meeting is booked, then assign it to the meeting owner. The Create record action needs a deal name and pipeline and stage, and associates the new deal with the enrolled record by default.
1. The action
Create record in my demo portal.
2. Avoid duplicates
Filter to the first booked demo so rescheduled meetings don't create extra deals.
3. Related
Meeting outcomes and Create record.