I also have stage-4 prostate cancer, and I'm also on ADT + Apalutamide for life (or at least until they discover new alternatives). As I've written elsewhere, my PSA has been undetectable (< 0.01) for 3 1/2 years. If I were to stop hormone therapy, my castrate-sensitive cancer might come back as castrate-resistant, and that's not worth the risk to me. If it's working, why mess with it?

As @jeffmarc mentioned, it's common with oligometastatic cancer (just a few metastases) to use radiation directly on the metastases rather than administering chemo, but obviously that varies from case to case, and you did mention the "potential for other metastases" — do you mean ambiguous spots of concern on the PSMA PET scan, or just a worry that there's more happening than PSMA PET can detect yet?