You can change your Outlook theme in your account settings while logged in through a browser or in the Mac and Windows apps.

Outlook Web App, also known as Outlook on the web, allows you to access your Outlook email account from a web browser.

Here is a complete guide to on how to add or change the profile picture of your Outlook account on Windows 11/10. You can follow this post if your Profile picture is not showing up in Outlook. How to ...