On March 15, 2021, users couldn’t sign in to Microsoft services the majority of the impact was with teams but other services were affected. A similar outage happened back in Sep 2020 (I covered it here https://www.youtube.com/watch?v=0ozri9APCv0&t=68s)

Microsoft 365 Service health status

https://twitter.com/MSFT365Status/status/1371546946263916545