Microsoft 365 is monthly subscription and you will get the latest updates for Microsoft Office Product and you will upgrade to the latest version of Microsoft Office as long as you have subscription and you have access to features which are only available in Microsoft 365.
However, Office 2016 is one time payment (not monthly subscription) and you don't have all feature which you have in Office 365. Latest version for the Microsoft Office is 2021 and 2016 is a bit old.