> But, there are some non-binary identities that I don’t have buy-in for. I will of course refer to people by their preferred pronouns to be kind, but can anyone give another reason?
In the general case your question answers itself. If you don't believe that someone is really (e.g.) a woman, then obviously there is no reason to refer to them using their preferred female pronouns except general politeness and kindness.
If I understand correctly, you are concerned about cases where someone does not accept either 'they', 'he' or 'she' as acceptable pronouns. I would urge you to find a real example, as discussing such cases in the abstract based on Wikipedia articles is frankly ridiculous. But again, the answer to your question in the abstract is obvious. If you don't believe that the person's identity is real, then you can either use their preferred pronouns to be polite – or not.
I fail to see any real philosophical issue that's raised here, given that you already accept that gender and biological sex are not inextricably linked. I guess there's the question of "How do I tell if someone's reported identity is real?", but that seems to be just a special case of "How do I tell if someone is being honest?". The answer is of course that you do so using your general nous.