Hello JoeFriday1979,
Welcome to Microsoft Community!
Regarding your concerns, it is recommended that you can click on the Filters drop-down menu, which should appear at the top of your inbox, and select “Unread Mail.” to filter all your unread emails, then please press to select one of the unread messages, when you see a tick in front of this email, you will be able to select multiple or all unread emails. After that, you can click click the “Mark As Read” button from the top toolbar. This will mark all the selected emails as read.
Hope above information helps. Please feel free to let me know if there is anything unclear or you have any problems when doing so.
Best regards,
Jennifer