Outlook M365: Modern Authentication and\or Password Prompt Control

The following is the summary of the above discussion.

Outlook M365 desktop app prompts for password and the classical methods for Outlook do not work for stopping it.

Further research has shown that while Outlook is accepting the password, it's updating a .tbres file in the profile directory AppData\Local\Microsoft\Token Broker\Cache.

Token Broker is a Windows process that helps manage permissions for apps and the Windows Store. It is implemented by the Windows service of Web Account Manager, described as:

This service is used by Web Account Manager to provide single-sign-on to apps and services.

This means that Outlook M365 desktop app uses the Token Broker process to store its credentials, which explains why the usual remedies do not work. The .tbres files are usually cited as containing (among others) credential information.

Outlook prompted for password when the poster purged <User>\AppData\Local\Microsoft\TokenBroker\Cache, although this stopped working after a reboot.

My last recommendation was to to automate deleting the .tbres file that was modified by Outlook, best done just before launching Outlook.