How to save the xmps for backup

You can make copies of the XMP files by using your operating system, but I advise against doing this.

Note: XMP files can only be considered partial backups of your work in LrC, there are many things in LrC that do not get written to xmp, hence this is why I call it a "partial backup". The full backup is to make regular and automated backups of your catalog file, using the LrC built in backup procedure. This will not back up the photos, these must be backed up some other way. Any backups you make, via any method, MUST (it is not optional) go on a different physical disk than the originals.    

Thus, in my opinion, backing up xmp files is unnecessary extra work that doesn't give full protection and doesn't provide any benefit over backing up your catalog file.  Backing up the catalog file is simple to automate and gives full protection.

• Are you referring to the XMP files that match the photo files? Those saved when you automatically wright changes to XMP?
• Then that would be backup the same way you choose to backup your photos?
• You do back those up correct? Remember they are not part of the LrC backup created (if you choose to do so) upon close of your catalog.

So, what you want is a backup application that you can setup to automatically backup files.

• How to back up catalogs in Lightroom Classic | Adobe
• Which Lightroom files do I need to back up? | The Lightroom Queen
• You're Probably Not Backing Up All of Your Lightroom Classic Data | Fstoppers
• What is a 3-2-1 Backup Strategy? | Segate