Microsoft is providing a new way to use the classic Outlook app on Windows and the Microsoft Edge web browser. If you have a Microsoft 365 Personal or Family subscription, browser links from the Outlook app will open in Microsoft Edge by default, right alongside the email they’re from in the Microsoft Edge sidebar pane. This allows users to easily access, read, and respond to the message using their matched authenticated profile. Links from Microsoft Teams messages will also open in Microsoft Edge by default in the future. Users have the option to turn off this feature in Outlook settings at any time.
https://support.microsoft.com/en-us/topic/outlook-emails-open-next-to-web-links-in-microsoft-edge-b0e1a1c1-bd62-462c-9ed5-5938b9c649f0