A family of Microsoft word processing software products for creating web, email, and print documents.
I agree that it does nothing, other than be very intrusive and annoying.
I am not on a Mac, and Bob is.
Others posting here indicate that sometime around January 24 a change was made to put a control in Word, but not yet other applications, to turn off Copilot. (Actually, to uncheck the default on option to enable Copilot).
My recollection is that it is under Word > Preferences > Proofing.