If you have an Android device or an Apple device with iOS 10 or older, modern authentication is not supported.
You must download the Microsoft Outlook app for your mobile device. Please use the following Microsoft documentation to set up Outlook on your mobile device.
For Microsoft Documentation, please refer here: https://support.office.com/en-us/article/set-up-email-using-the-ios-mail-app-7e5b180f-bc8f-45cc-8da1-5cefc1e633d1