Starting in July 2021, users who have activity history synced across their Windows devices through their Microsoft Account (MSA) will no longer have the option to upload new activity in Timeline. They'll still be able to use Timeline and see their activity history (information about recent apps, websites and files) on their local PC. AAD-connected accounts won't be impacted.
The User Activities feature allows apps to create and publish Windows-style User Activities.
User Activities are cloud based constructs that track the state of a user's tasks in an app. Activities can be viewed and resumed at a later time, even across different devices and platforms. For more information on User Activities, see Continue user activity, even across devices (UWP).
To get started with User Activities on your device, select your preferred development platform on the left navigation pane.