Try reinstalling CCleaner to see if it picks up the change then.
Download an installer from here: Download CCleaner builds | CCleaner Portable, Slim, and more
Double click the downloaded installer to reinstall a fresh CCleaner.
Don’t uninstall the old one first - that way the new install will pick up your settings, licence key, etc from the old one.
If it still shows Win 10 then you could then try an uninstall/reinstall, renember to make a note of your settings and licence key because you will have to put them back yourself.
Just to check; this is a fully compatible machine for Win 11 and you haven’t used the workrounds to update an ‘unsupported hardware’ machine?