Sending, receiving, and organizing email in Outlook.com
Other users are reporting the same issue, which could be a server-side error. There is currently an Exchange error, and multiple users are also reporting Outlook outages.
https://status.cloud.microsoft/
https://x.com/MSFT365Status/status/2094455556454920701
The link above is not an official Microsoft site; however, it is related to the post on the official X page reporting the outage.