Using classic Outlook for Windows in business environments
If you still have office 2016, uninstall it and install 365. Or use the method in this article - hhttps://www.poremsky.com/office/remove-office-licenses-windows/ - to remove the 2016 license. Then sign in with the office 365 subscription - but if you have the 2016 license in the Microsoft account, it might pick it up. In that case, you will need to uninstall/reinstall.