Windows 11 Installation Assistant - Windows 11 Installation Assistant (Windows 11 Update Assistant) is designed to prepare your computer for upgrading or updating Windows 10 by checking for compatibility issues and downloading all necessary files to start the install.
While Microsoft Windows 11 Update Assistant can check your computer to see if it can run Windows 11.
Beyond that, Windows 11 Update Assistant is geared towards advanced users and IT departments looking to get the latest large updates, for example, the Fall Creators Update.
In other words, Microsoft Windows 11 Update Assistant can download updates that are available but not in your Windows Updates yet. Everyone will eventually get the larger updates through Windows Updates.