Robocopy is a command-line utility that can be used to mirror the source data for the backup. It can copy files and folders with various options, such as copying only changed files, preserving attributes and permissions, and retrying failed copies. Robocopy is more powerful and flexible than copy or xcopy, which are simpler commands that can only copy files and folders without mirroring or other advanced features. Copy-Item is a PowerShell cmdlet that can also copy files and folders, but it is not a native Windows utility and it requires PowerShell to run1.
References: 1: https://windowsreport.com/mirror-backup-software/