Even "disharmony" is far more common than "disharmonious."
"And a sea of pulchritudinous models would have served as a lesson on how not to choose words: the ugly pulchritude sounds like the opposite of what it means, and it is one of those words that no one ever uses unless they are trying to show off.” https://www.goodreads.com/work/quotes/40167209-the-sense-of-...
That said, as a french speaker I would have had no idea what this word means if I did not took Latin in high-school.
To me, pulchritude is such an ugly sounding word I can always remember the meaning as being the opposite of how it sounds.
(Funny enough, I was just looking up to see if there is a name for words that sound opposite to their meaning and found this [0] discussion on the English stack exchange, which gives pulchritude as its example!)
[0] https://english.stackexchange.com/questions/103741/name-for-...
A guy with an unshaven face, wild hair, casual or wrinkled clothes, etc would never be described as "pulcro", even if they otherwise look very handsome, beautiful, or attractive.
* https://www.dl.cambridgescp.com/dl_course/book-i
A random other example: https://www.ocr.org.uk/Images/221512-gcse-latin-j282-defined...