Hello Scott,
Greetings. Hope this finds you well.
According to your description, I really understand that you are referring to difference in the current feature in New Outlook preview and the classic outlook. And based on my research, I got the same result as yours, I didn't find a way around this in the new outlook especially adding a note to the task. Currently in the new outlook, you can only use the My Day pane to create a task from an email message. (Open the My Day pane by selecting
My Day on the toolbar at the top of the page >To do >Find the message that you want to create a task from in the message list >Select and drag the message to the To Do tab in the My Day pane).
I do understand your need for this, and we will surely raise your concerns with our product team and hopefully this can be included in future updates. If you heavily rely on this feature, you may consider toggling out of the new Outlook for Windows preview for now.
Please kindly understand that many functions are not designed at present. I'd suggest creating an entry as a feature suggestion in feedback collection directly through your new outlook (Help-->Feedback) or at Outlook · Community (microsoft.com) and many other users could vote for it. Many features of our current products are designed and upgraded based on customers’ feedback.
I will update here just in case I get any update on this.
Thank you for your understanding.
Best Regards,
Ashraf.