An extension of the mess that is MS Identity
You'd expect that a giant like Microsoft would at least be able to come up with a consistent approach to identity, but this split personality "microsoft account" vs "work or school account" is about the stupidest and most infuriating solution you could every hope to see. I can't begin to describe the frustration of trying to login to a service using my Microsoft 365 account and being told "that microsoft account does not exist". *I* know that's because my 365 account is actually an Azure AD, sorry, Entra AD account, and a Microsoft Account is actually a Windows Live account, but try explaining that to someone non-technical. The Identity team at Microsoft should be ashamed that this mess is the best they could come up with.