@iturnedintoanewt@lemm.ee and @JeyNessuno@lemmy.dbzer0.com register on MacBB and search for Office 2021 it will provide you with everything you need.
It boils down to downloading Office from Microsoft itself and using a Volume serializer (also provided by MS to big companies) that will add a valid and permanently activated license to Office and updates work without issues as all. Microsoft doesn't care much about Office for Mac piracy there isn't a KSM protection and licensing scheme like under Windows.