Short answer
HubSpot's KB: after connecting the Zoom app, add Zoom to your meeting links. Your HubSpot user email must match your Zoom user email; verify the connected Zoom user in settings.
1. In HubSpot
The relevant screen in my demo portal.
2. Worth knowing
Mismatched emails are the usual reason Zoom won't appear as an option.
3. Related
Meetings links and Notetaker in Zoom.