Using New Outlook on Windows for professional communication and productivity
Joanna, they don't tell you this, but when the new Outlook (including Calendar) app opens there is a toggle button in the top right corner that allows you to move between Outlook and the old Calendar and Mail apps. Each time you open Mail or Calendar now it automatically diverts to the Outlook app but flicking the toggle switch will close that app and reopen the old apps. P.S. If like me your old calendar app entries do not appear in the new Outlook app calendar because that app does not support IMAP yet you can bypass the Outlook app and access your calendar by logging into https://outlook.live.com/ (or outlook.com) via a web browser (i.e. Edge, Firefox, Google) then navigating to Calendar.