In the latest Windows 11 Dev channel preview build 26300.8289, Microsoft has replaced the login/logout/restart loading animation that has been used since Windows 8. The new animation is consistent with the loading indicator that appears when Win11 is started, replacing the old rotating circle that has been in service for 14 years.

This change has not been officially announced yet and needs to be manually enabled through the ViVeTool tool. The steps are as follows:
Download ViVeTool from GitHub and unzip it. Open the command prompt as an administrator and navigate to the directory where ViVeTool is located. Enter vivetool /enable /id:59728252 and restart your computer to experience it.

Old animation
Windows 8 significantly restructured the system UI when it was released in 2012, but some legacy elements still remain in Win11.
Microsoft has been promoting the modernization of the Win11 interface in recent years. This replacement of the loading animation is a small step in improving the consistency of the system UI.
Microsoft’s current Win11 fix list also includes higher-priority projects such as Windows Update improvements, new taskbar features, a faster file manager, a clearer Insider plan, and more stable update push.