Unauthorised logins appearing in Apple Keychain, specifically Microsoft online logins.

I started noticing strange Microsoft logins in the iCloud passwords app about a month ago. No idea where they come from but when I delete them they re appear in a few days. These login details also appear on the Microsoft online login options, along with my own known options, as “saved” MS login addresses but they aren’t visible in my MS account profile. I only have one account for the MS Authenticator and a passkey is set up in my Keychain for the MS login. There’s nothing untoward going on in my online MS account and the login history shows nothing untoward either. My only explanation is that a hacker has gained access, but I’ve no idea how or why? Any ideas would be gratefully received.