iPhone Back Up Storage
Did you recently uninstall and reinstall iTunes from the Microsoft Windows 10 store? If so, the location of the backups may have changed, causing the backup to not be where you expect it to be.

Here's a blog post I wrote with instructions to get to both locations where the different versions of iTunes store the backups on Windows 10. (The different versions being direct download from Apple and download from the Microsoft store.) Hopefully checking the "other" spot will help you find the backup that is hiding from you :)

https://deciphertools.com/blog/where-are-iphone-backups/

If you don't see anything, you may need to allow showing hidden files. https://support.microsoft.com/en-us/help/4028316/windows-view-hidden-files-and-folders-in-windows-10