I cannot sign in, after clicking on the button it displays a message "We couldn't sign you in. Please try again." and when I try again this repeats indefinitely. I have tried this both on Firefox and Edge and it doesn't resolve. Meanwhile, the app can't load at all, after some time it displays a message "We're sorry - we've run into an issue. Try again. If that doesn't work, try signing out and back in." which I have tried with the same result.
However, Teams on mobile works just fine without any complications.
I have also posted the same question on answers.microsoft.com and an agent advised me to post it here for more help.