Dear John,
Thank you for your reply.
We see you are actually in the New Outlook.
Please understand the new outlook is still in preview state and there some features updating is still on pending. the 'Flag for recipents' is currently not supported in new Outlook and If you need recall message, the quickest work-around is to go into the email you want to recall and type "recall" into the search field at the top that reads "Tell me what you want to do." You can then choose the recall option that works for you ---- delete unread message or delete and replace with new message. Also, you can switch to classic Outlook by clicking the****"Try new outlook" off.
We are sorry for the inconvenience it may cause and appreciated for your understanding, meanwhile, our product team would like to hear your voice on New Outlook, you can go to Help-->Feedback to submit your voice.
Thank you for your understanding and cooperation
Microsoft Community