>>11387308 (PB) Outlook Login Problems

Microsoft disabled older login methods (see below) – I think they disabled Modern Authentication and you now have to use OAuth – affects most older versions of Outlook installed locally

Per Email received by my email provider

Head’s up: As of 20 October 2020, Mail will no longer support third-party applications (such as third-party email, calendar, or contact applications) using outdated sign-in methods. That just means if you’re still signing in to your account via another email application, like the default email application on your phone/computer, you need to make some quick updates to ensure your mailbox isn’t interrupted.

Option 1: We recommend that you access your email using our free online app

Option 2: Follow a few steps to get it to sync with our secure sign-in method. The steps vary across different email applications, but in most cases, you will have to remove your account from the app and then add it back again to update the sign-in security

Option 3: You can generate a one-time, unique password that will allow you to sign in to your account using your local email application

https://docs.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/outlook-for-ios-and-android/setup-with-modern-authentication