Short answer
HubSpot's KB: the connector is read-only. It fetches contacts, companies, deals and their associations into Gemini, and users only see records they can access in HubSpot. It works in the Gemini app and in Google Workspace.
1. In HubSpot
The relevant screen in my demo portal.

2. Worth knowing
Updates still happen in HubSpot itself.
3. Related
The ChatGPT connector and connectors and sensitive data.