Observing the code example from pqcrypto-kyber, is the decapsulate function $d$ homomorphic?
If $d(ct, sk_i) = ss_i$, is it true that $d(ct, \sum_i sk_i) = \sum_i ss_i$ ?
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Kyber claims to be CCA secure. CCA schemes cannot be homomorphic (thinking through this may be a useful exercise).
It may be useful to try to work through this particular example with pen and paper by looking at algorithm 5 in the Kyber paper. Note that what is returned is some hash, which you should not expect to have homomorphic properties.