https://www.bleepingcomputer.com/news/microsoft/microsoft-shares-workaround-for-outlook-freezes-slow-starts/ > Microsoft is working to address a known issue affecting Outlook for Microsoft 365 customers, causing slow starts and freezes as if Offline Outlook Data Files (OST) are being synced right after launch. > However, no new OST files are being created, and no new entries associated with this behavior are added to the Application event log, according to Redmond's investigation.