https://www.bleepingcomputer.com/news/security/rsat-will-automatically-be-reinstalled-after-new-updates-in-next-windows-10-version/

In Windows Insider Preview build 17682, Microsoft has made the Remote Server Administration Tools (RSAT) an on-demand software feature. What this means is that once you install RSAT in Windows 10, it will be automatically reinstalled when you install a future operating system update.

RSAT is a tool that allows administrators to manage Windows Server from a remote computer running Windows 10. For some time, Administrators have been complaining that when you install a new upgrade of Windows 10, the installed Remote Server Administration Tools would be removed. This is because each version of RSAT is tied to a particular version of Windows and thus you need to download and install the correct version for it to work properly.