I faced the same problem today in my Edge browser.
Then I checked my mailbox from and Android Chrome browser and it worked fine.
Then checked my mailbox from Firefox browser on Windows and it worked fine.
Therefore, I suggest you try with a different browser as a workaround.
I'm guessing the problem is related to some malformed cookie, thus probably if we were to clear the cookies from the browser where we see the problem, then probably we would be back to a usable Outlook again.
Let me know it this helped.