I have found (with over 50 Microsoft Accounts) That short of using 3 different versions of Edge, 1 of Firefox, 1 Chrome etc. etc. that the easiest way to log out of an account is using the Azure Portal and selecting Log Out.

Microsoft are really only motivated by apps that matter. Sharepoint is a dog product and always has been. It brings down the the whole of 365. Fancy still not being able to deal with text files, I mean what is that?

Oh, and if you don't have access, it can't tell you who you are before you ask.

So, portal.azure.com, it does not matter if it is a mess, you can sign out an sign in as a different user.

Microsoft, you need a web app that does this and nothing else.