Dear Amanda Goodness,
Thank you for posting in Microsoft Community.
According to your description, in Outlook Web App I only found one similar feature: “previous” and “next” buttons. These 2 buttons appear only when “the reading pane” is hidden:

If I turn on the reading pane, these 2 buttons won’t show up in Outlook Web App and I need to use up and down arrows on keyboard to switch to previous and next emails.

Please check if you’re in the same situation. If you have different scenario, you can share more details with me ( like one screenshot) so that I can compare it on my side for checking. We look forward to your reply.
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Sincerely,
Etta Ma MSFT | Microsoft Community Moderator