Using Classic Outlook on Windows for personal email, calendar, and contact management
I confirmed yesterday that this has been partially fixed in the latest preview. HOWEVER, there is some weird issue where often it doesn't properly detect a double click, and the single click results in the behavior we can't stand, and it opens the email in the main window, making the inbox disappear. So far I've not seen an option to get rid of that.
The behavior needs to be the same as Outlook has been for literally decades... a single click highlights the message, a double-click opens the message in a separate window.