I'm sorry to hear that. My cancer team told me that if/when my ADT+Erleada stops working, there are "lots more" things to do these days — those are just the start of the treatment journey, not the end.

If you're doing your own searching, the keywords you want are "metastatic castrate-resistant prostate cancer" (or "mCRPC") — those will give you the most-relevant results.

I assume he's already had radiation to his prostate, but if not, that's one option. If he has only a few metastases ("oligometastatic"), then they can zap them as well; otherwise, there are treatments like Pluvicto for mCRPC that he can take in liquid form to deliver radiation to lots of small metastases internally. Then, of course, there's chemotherapy, PARP-targetting drugs, and probably lots of other treatments I can't think of right now.

I'm looking forward to reading what others post, because this may be in my future as well if/when my stage 4 prostate cancer becomes castrate-resistant.