To get you started, this is how in my Movies library with librarySectionID=“1” I could do the initial search, assuming my token=1234567890abcdefg, in BASH.
curl -X GET "http://127.0.0.1:32400/library/sections/1/all?X-Plex-Token=1234567890abcdefg&sort=userRating:desc"
Items that you never rated are missing the userRating field entirely.
Whether that’s equal to userRating="0.0" I’ll leave as a treasure hunt.