MacOS – Closing Preview documents without confirmation dialog AND without quitting Preview

Is there any way to close "Untitled" Preview documents without getting the confirmation dialog box (where it asks "Do you want to save the changes made to the document ….?")?

I don't want to just quit, or force quit, the Preview program, because I often have some other documents open that I want to combine and/or save with different names LATER.

I've tried un-checking the General System Preferences option "Ask to keep changes when closing documents", but that didn't work, even after a reboot. And there doesn't seem to be anything relevant in the Preview preferences.

I just want to quickly close a bunch of untitled documents so I can free up some memory or reduce clutter, without having to mouse over to each individual dialog box and click "Don't Save".

If that isn't possible, here some ideas for other methods that would also be helpful – I just don't know if they're possible either:

A. Select a bunch of Untitled documents in a multiple document Preview window and:

1. Close them all at once without saving any of them.
   (There is a File menu option for "Close Selected Documents", but it opens up a separate confirmation dialog box for each one.)
2. Save or Rename all of them all at once (i.e. Untitled1, Untitled2, etc). Then if I have the General Systems Preference "Ask to keep changes…" unchecked I could close them all at once by closing the multiple document window.
3. Combine them all into one document. (I know you can use Print to convert them into a single new document, but you still have to close the original separate documents).

B. Use a keyboard shortcut for the "Don't Save" button, so at least I can get through all of the separate dialog boxes more quickly.