@Spencer Ian, Agree with Michael, the Windows.old folder is automatically created during a major Windows upgrade to allow rollback to the previous version. Unfortunately, there is no built-in way to suppress the creation of this folder during the upgrade process, as it is a safeguard feature of Windows.
Just as Michael mentioned, the Windows.old folder is automatically deleted after 10 days by default. If you want to clean it directly, here are two links with the commands to do this. You can read them as a reference.
Note: None-Microsoft link, just for the reference.
Hope the above information can help.
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