I see several people say primates don't show the effect, however all tests on primates were done with a "language-competent bonobo" and "touchscreen trained chimpanzees (N=6) and gorillas (N=2)" that are first trained to do various language/picture association tasks and then tested like how you'd test humans. It would be interesting to test primates using the same methodology they used here on chickens. The previous language/computer training in the monkeys might have interfered with a more low-level/intuitive bouba-kiki effect.

References here https://evolang.org/jcole2022/proceedings/papers/JCoLE2022_p...