Why doesn't Disk Cleanup show "Previous Windows installation(s)" on Windows 10?

That option only appears when Windows detects an old installation it can clean up. A large update doesn’t necessarily create one—monthly cumulative updates and some feature updates don’t leave a full Windows.old folder.

Since you’ve already tried Clean up system files, check these next:

1. Open your Windows drive, usually C:, and look for C:\Windows.old. If it isn’t there, the upgrade may not have created it, or Windows may already have removed it. The rollback files are normally cleaned up after the rollback period, usually 10 days.
2. If it exists, go to Settings > System > Storage > Temporary files, let the scan finish, and look for Previous Windows installation(s) there. Review the selections carefully—Downloads contains your own files.
3. Before removing an old installation, check Windows.old\Users for anything you still need. Removing it also removes the files needed to go back to the previous Windows version.

If neither cleanup interface lists it, don’t assume the list is corrupted or force-delete it by taking ownership. Check whether the folder actually contains substantial data. If your missing space is elsewhere, Settings > System > Storage can help identify the category; Windows Update Cleanup is separate from previous-installation cleanup.

Don’t manually delete WinSxS or other Windows system folders to recover the space.