Mac New Outlook and Office Insider reply button problems

When I want to reply to an email the reply or reply-all button don't work when I read the email in the main Outlook window.

However when I open the message in a separate window (ie double click the message) then the reply and reply-all buttons do work. I do notice the design of the message when opened in a separate window looks like the old Outlook (the ribbon icons do not look modern).

When I switch back to the classic Outlook there is no issue.

Running Outlook 16.47 on Mac OS 11.3