Hi Nebucadneza
Thank you for providing that information.
We have tried to replicate this on our end and unfortunately, we also are unable to drag and drop mails into desktop from the new Outlook. This could be due to the new Outlook that is still on preview channel.
With that being said, we highly recommend that you provide feedback directly to our developers within the application. Since the new Outlook is still on preview, as expected there are still lot of changes with the functions and features. So it is better that you provide feedback about this matter directly to our developers.
We’d love to hear from you about what’s working well, what’s not, and any ideas for improvements including possible new features and functions. You may refer to this link here on how you can provide feedback. How do I give feedback on Microsoft 365? - Microsoft Support
We appreciate your understanding.
Sincerely,
ReynaldoB
Microsoft Community Forum Moderator