Bug : Teams notifications not going away despite message being opened

Hi, do you mean the Mac notification centre - from the top right of the Mac desktop? If so, I find that notifications in here don't always match the action you take in the actual app. Seems to be a quirk of Mac OS as far as I can tell. Take a look at the settings in System Preferences > Notification Center and see if anything in there may alter this experience. I personally don't use the Notification Center I must admit as I prefer to respond to apps by the badges that are presented when a new item comes in.