I think you can still do that. If I get correctly what you are after: Start the process of creating the smart collection and when you see the pop-up list of parameters to select from to create your collection, scroll down to "Other Metadata" click on it and you will see "Keywords" there. I hope this helps
Thank, you! That works. When you do it, the "Keyword" rule type then
appears at the top level of the menu. Very well hidden. The relationship
between LR keywords and photo (EXIF?) metadata is not obvious.
(I also found a workaround: Export smart collections settings, edit the
resulting JSON-like text file if needed, then Import it into Collections or