After upgrading to Windows 11 from Windows 10 or another version, you will probably notice a spike in storage usage. Use these steps to get the storage back.
When you upgrade to Windows 11 from Windows 10 or another version, the setup makes a copy of the previous installation as part of the process, in case something wrong happens during the installation, and the system needs to roll back to the original setup, or Windows 11 is having compatibility issues, and you need to revert to a previous version manually.
Full story from the WindowsCentral blog...