Microsoft's To-Do app is one of the best productivity tools in their new line of multi platform apps. The most recent update includes flagged emails. It runs on Win 10, Android, and IOS and integrates with Office 365 / Exchange Tasks.
I've never been a fan of the generic MS task view in Outlook, but the new To-Do overlay makes it dramatically more useful. Give it a try at.https://todo.microsoft.com/en-us