Anyone who has ever done development on any Microsoft site has felt the pain of a million logins.
I was working on Outlook stuff at my previous job and it was a nightmare. They have three different offerings of emails. You can login in Outlook and O365 with the same account iirc, but not the others. Or something like that.
I just remember wanting to cry as I tried to figure out how to login.
Then the API docs are even worse. They had different APIs for each email offering and one pointed to the other then that one pointed to the previous one.
Microsoft's problem is that it has too many services. Google may change things constantly but at least they don't have three different email offerings with three different APIs at varying levels of brokeness.
Why on earth are there so many domains in their login flow? My password manager can't make heads nor tails of it 90% of the time