A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
OK, I tried again.
Double checked that the option was unticked - it was.
Opened one file - no message - "great", I thought!
Tried another file - and there's the message again.
I even tried a complete reboot, just in case - no luck, still got the blasted backup to OneDrive message.
FYI, I'm on Win 11 Home, all updates done, version 24H2, build 26100.3775
Update: strange thing is, the message only appears on some Word documents (all of which are on my local drive). Consistently the case. Weird.