Outlook disconnected from the server due to various reasons. It might be caused by a temporary network glitch or a problem with your internet connection. Additionally, server maintenance or updates can lead to a temporary disconnection. Incorrect account settings or expired login credentials could also be culprits. Firewalls or security software may block Outlook's access to the server. Furthermore, if the server itself experiences technical issues, it can result in a disconnection.
https://comfix365.com/blog/outlook-disconnected/