I haven't had to use this option since, I think, version 5.44 or even earlier, so I'm not sure when it disappeared.
Was this an oversight or a policy decision? It was certainly convenient. If you try to delete the Old Windows installation folder after the biannual update (like, right now, for instance) you have to sit there and watch it, interminably, so you can field any "helpful" questions from the system that stop the process. When CCleaner did it, it just did it and you could walk away during the entire long process.
Cleaning the windows.old folder breaks windows for many people. Some of the stuff in the folder are still used by Windows and slowly are migrated out. Use windows inbuilt cleaner to remove window.old (if storage sense even does that now that cleanmgr is gone).
The cleaning of windows.old by CCleaner was first removed in version 5.45.
Unfortunately the changelog for v5.45 was taken down when 5.45 was withdrawn, so the removal of that option may have escaped peoples notice.
It is mentioned elsewhere in other threads.
If you run Storage Sense 'Free up space now' then you should see it scanning for "Windows Update Clean-up'...... BUT-
Unfortunately Storage Sense seems to be broken on my 1809 and isn't scanning at all?
(Disk Clean-up is still working and finds 'Previous Windows installations' at 26.7GB on my laptop)
EDIT- SS is in fact scanning and will find 'Previous Windows instalation(s)' - it's just taking it's time to show anything on the progress bar when it starts scanning.
Leave it a while and the progress shows, and the list of things to be cleared is populated.