Not to say that Microsoft products respect privacy, but I don't see evidence that user Word/Excel files are being used for training.
The linked services agreement has had the same language (copy/transmit/etc. "to the extent necessary to provide the services") since at least 2015[0], and "connected experiences" seems to group a wide range of integrations; some like dictation/translation probably utilise ML, but that does not mean training on user content.
[0]: https://web.archive.org/web/20150608000921/https://www.micro...