Read the M365 EULA
In July 2020 The Register, our usual source of unbiased news (ahem), ran an interesting piece on a pending court case against Microsoft in California. Within the article the actual complaint document was linked via courtlistener.com, to wit: https://www.courtlistener.com/recap/gov.uscourts.cand.362635/gov.uscourts.cand.362635.1.0.pdf.
This thing makes for good, if somewhat dry, reading. It's information straight from the horse's mouth, though; you might be …