You mean those sketchy Office 2021 Professional Plus deep discounts, right? That's an (expensive) edition available in MSDN-like subscriptions, I'm almost sure they're either "cheap region" keys or MSDN-generated ones. Some of the worst offenders even tell you you'll get a username and password in an email (rather than product key), confirming it's just a user in their 365 tenant. (Of course I'll hand my documents off to CheapOfficeDotCom)