Sounds word-for-word like my father. And your situation sounds like mine. I have moved abroad, and I still try to support him, even if it's just giving him time to talk on the phone and sometimes vent. I try to be compassionate as much as I can, despite how difficult it is.

Sometimes I think of it as a Jekyll and Hyde situation, but where Jekyll isn't some average nice guy, but someone who is extremely loving, curious, and altruistic. When Hyde comes out, as briefly as he does, he's miserable, angry, and emotionally destructive. The switch can happen almost instantaneously. Nowadays, Hyde comes out less and less, but it took work to get here. I myself don't know for certain if my father fits the narcissistic personality definition. It makes it even more difficult because people often make suggestions like completely cutting him out of my life, which I'm not keen on doing.

I only managed to have the conversation (that, similarly to your father, my father also tries to shut down each time) this year. It was after a heated fight, and I was furious, depressed, angry for a long time. For the first time ever, I called him back and demanded to talk to him even after he's calmed down himself and tried to move on. I said I wouldn't move on before we spoke in-depth. For the first time ever, he listened to me in full and apologized sincerely. Now when he has one of his explosive episodes, I refer him back to this conversation. Has this fixed everything? Not at all. But at least there's progress, which means things can get better. My step-mother too sounds less stressed when I talk to her. I wish I had this conversation with him earlier.

I don't have much advice, besides being patient with yourself. If patience fails, don't beat yourself up. You deserve to fully feel your own difficult emotions. And don't let anyone ever gaslight you by telling that it's not too bad because he's not like that all the time. Or that somehow you are the blind victim of your father's diabolical scheme to appear better than he actually is. Both sides can be real. People are complicated.