Using classic Outlook for Windows in business environments
I have found somewhat of a work around: click on the 'gear' icon, scroll down in settings to the 'reading pane', select 'right' or 'bottom' whichever you prefer. This shows the list of emails that you can work through instead of always having to go back to the list after reading an email.
I hope the up and down arrows will return, but until then, this work around has been helpful