When he is off the reservation saying whacky things. Be neutral and disengage..perhaps mention you are available later to listen and understand.
Could you provide an example? I am a fairly practical learning and it would be helpful to hear what someone else may say.
When he is "normal" or "positive"..then "lean into" the relationship...go overboard..tell him how awesome he is..etc etc.
I think this is what has been missing! Why is this not happening as much? Hmmm... something I need to reflect on.