I have the same problem, but it does not relate to whether the email was received immediately following the install, or whether the mail has been previously read. Outlook hangs with a spinning ball when certain messages are selected in the message list and displayed in the preview pane. Display of the message is only partial and then Outlook hangs with the partly displayed message and the spinning ball. Force Quit is required. It appears to relate to the content of the message and whether the message contains a URL and or/and an image. It does not happen with pure text messages. It always happens with messages that contain unreachable urls. It sometimes happens with other messages with urls/images. It happens persistently with any email for which it happens once. Force Quit does not resolve the issue for affected messages. Previewing such messages after Force Quit and reload of Outlook will yield the same result. The same problem can be created by right-clicking the message in the message list and attempting to forward it. It appears that the problem relates to parsing the content of the email message for display or forwarding.

Auto-resolved - see above

Problem auto-resolved after shutdown and restart - unsure why, as nothing had changed.

Same here between 2 Macs running Big Sur beta 6. Don’t get an authentication error, though - get a message saying “There was a problem connection to the server <hostname>. Contact your administrator for more information.” Console shows error “netfs_GetServerInfo returned 5” Can connect to the shares on both Macs from Windows 10. Can’t connect from Mac to Windows 10; same error as above.