Copilot sees what you can see, no more and no less. It grounds answers in Microsoft Graph, and Microsoft states that it only surfaces organisational data you have at least view permission for. It relies on the same access controls as SharePoint, OneDrive, Outlook and Teams, so it never overrides them.
The catch is in the word "can". Old, loosely shared folders that nobody remembers granting access to are within reach too, and a broad question can bring them back up. Copilot did not create that exposure; it removed the friction that kept it harmless. That is why the track treats a periodic look at what is shared across your tenant as part of using Copilot responsibly, the practical side of the EU AI Act's Article 4 AI-literacy duty.