"Microsoft offers workaround for Outlook's slow startup and freezing issues"
Microsoft is investigating and working on fixing an issue affecting Outlook for Microsoft 365 customers, causing slow starts and freezes during cache re-priming. A workaround is available by toggling on the "Shared Calendar Improvements" option in the Exchange Account Settings dialog or using a group policy setting to enable Outlook REST calendar-sharing updates. Microsoft has also fixed other issues with Outlook in the past, including login issues and freezing and crashing right after launch.