Dear Jonathan Brotto1,
Good day! Thank you for posting to Microsoft Community.
To open a new message window instead of showing up in the message pane on the right, you may need to change the Pop-out setting in your new Outlook settings. Here are the steps to follow:
- Open your new Outlook --> Settings (the gear icon at the right top corner) -->Mail -->Compose and reply -->Under Pop-out settings, select Pop-out to a new window option -->Save. Then, check if there is any difference. You can refer to the screenshot below:
I look forward to your update. Please feel free to let me know how it goes or if I got you wrong. If you still have any concerns, please let me know so I can provide more suggestions.
Thank you for your precious time. Have a nice day.
Sincerely,
Libeamlak | Microsoft Community Moderator