3. Cryptographic primitives. Curve25519 / XSalsa20 256 / Poly1305 (downgraded for the absence of PQ encryption).
We added PQ encryption in March this year: 
This is done in the same way as Apple describes as PQ3 here: 
it provides stronger protection than Signal design where PQ encryption only applies to the initial key exchange.
SimpleX Chat v5.6 (beta): adding quantum resistance to Signal double ratchet algorithm
iMessage with PQ3: The new state of the art in quantum-secure messaging at scale - Apple Security Research
iMessage with PQ3: The new state of the art in quantum-secure messaging at scale - Apple Security Research
We are introducing PQ3, a groundbreaking cryptographic protocol for iMessage that advances the state of the art of end-to-end secure messaging. Wit...