Desktop operating systems aren’t built for single users. We may have laptops that are exclusively used by one person but the operating system they run can support multiple users. For each user that you add, a separate user folder is created and the user gets their own libraries and their own system settings including a wallpaper, default apps, and their own Start menu layout. More info at https://www.addictivetips.com/windows-tips/sign-out-other-users-windows-10/