[jiiam]

I think this statement requires a stronger argument, since even if they could have access to the data in theory there are concrete implementations where it could be extremely unfeasible.

For example, since we are in the realm of speculations, I propose the following alternative to the plaintext or accessible decryption keys: the decryption could happen inside a nitro enclave making it essentially impossible to access the data without changing the application code.

I'm not saying that this is what happens, just that I don't think that one can so easily deduce that "they can access the data" just from the fact that "they send you chat history to you".