Thankyou Ian, this solved my issue!
Note to others following this solution, at the page linked below, click on the 'privacy settings' link within the page to find how to access your privacy settings, then uncheck the four 'Connected experiences' options. Restart required.
Col.
Hello Ben,
I understand the concern and inconvenience this change causes.
Since Copilot is a connected service, it is my understanding that disabling the Microsoft 365 online experience accomplishes the same thing.
Please see Copilot in Microsoft 365 apps for home: your data and privacy - Microsoft Support

But this can also cause other online services to be unavailable. In the meantime, click File->Feedback in the Office app to let Microsoft development team hear your valuable thoughts.
Sincere greetings,
Ian - MSFT | Microsoft Community Support Specialist