Welp, I have just cancelled my Microsoft Office 365 recurring subscription.
Two reasons.
1. I only ever use it to check tracked changes to the copy edits on novels—once a year—which my publishers process in Word. As of this month, LibreOffice is good enough for the job (just tested at book length).
2. CoPilot in Office would open me up to accusations of breach of contract—my book contracts warrant that they're all my own work: CoPilot brings that into question.
So good riddance to Office365!