Using Classic Outlook on Windows for personal email, calendar, and contact management
Same problem for me. Clicking on the pop-up notification does not open the email and the 'delete' and 'flag' action buttons do not work. Clicking on the email from the notification center simply removes the notification. Running Microsoft 365 for Enterprise, Version 2005 (Build 12827.20336 Click-to-Run), which is the May 2020 update. Windows 10 Pro Version 1903.