Office 365 (Web) - Outlook Light
If your Outlook looks like the image below, you're in the light version of Outlook. This means you're using an old browser that's incompatible with the new Outlook.com and Outlook on the web or with Outlook Web App. To check to see if your browser is up-to-date on your personal device, go to https://updatemybrowser.org/. For the best experience, please update your browser to the latest version. To get to the standard version of Outlook, sign out of your account, update your browser, and sign in again.
For more information on Outlook Light, please reference the following Microsoft help article: https://support.microsoft.com/en-us/office/learn-more-about-the-light-version-of-outlook-2aec8c2d-da48-4707-ba37-c800e1c284cd