From Microsoft Corporation
Technical Bulletin MC301007 · Published Nov 30, 2021
Message Summary
Beginning February 2022, the list of “Application Users” will no longer be available under Advanced Settings in the Dynamics 365 legacy web client. This change will occur as part of a service update during your regional maintenance window.
How do I prepare for this change?
We recommend you become familiar with viewing and managing Application Users within the Power Platform admin center. Please see Manage application users in the Power Platform admin center for more information.