My starting PSA was "only" 215, but that in itself indicated widespread disease, which was very quickly confirmed by all the testing.
Stage 4, mestastisised extensively, Incurable, aged 53.
So in November 21, I was exactly where your dad is now.
1 month later PSA was 3.6.
Next month was 1.6
Next month was 0.02 and that's where it had stayed to the present moment, 32 months later.
There is hope, if not a curative intent.
My overall advice is stay positive, keep fighting, none of us know what new treatments are being developed that might cure or extend life!