Almost everything you read online about stage 4b prostate cancer is out of date now (assuming you're getting the latest treatments). I'm not trying to be a Pollyanna and pretend there's nothing to worry about — stage 4b is a tough ride — but prostate-cancer treatment has gone through a seismic shift in the past 5+ years. As an article in last month's Scientific American said

«These new strategies have begun to transform this once rapidly fatal disease into a chronic condition that people can live with for years or even for their full life expectancy.»
https://www.scientificamerican.com/article/treating-prostate-cancer-at-any-stage/
So while there are no guarantees, it's no longer naïve to keep hoping. When I went to the Canadian Cancer Society's website to read about stage 4b when I was initially diagnosed in 2021, the advice was basically "Learn acceptance, put your affairs in order, and prepare to die" (in more-polite words), which was awful to read; fortunately, within a year my onco team was telling me a very different story.

Will I make old bones? Maybe not. But it's no longer a pipe dream.