Google一下
The $WinREAgent folder is created during a Windows Update or upgrade and contains temporary files that allow you to recover Windows 10 if there are problems during the upgrade or update.
总结一下:
$WinREAgent 文件夹是WIndows10更新是产生的, 用于存放更新失败恢复的文件. 更新之后可以随意删除.