I ended up on this page which I no longer remember (something something prostatitis foundation maybe?), from which I remember two things.
The first was this turkish doctor, who against all advice was suggesting a "Brocolli juice therapy" as a prostatitis cure. Fast forward to 2025 and there's lots of studies supporting this. Anecdotally I tried this back then and it really helped the prostate pain I had at the time for months go away within a week.
The second, which is more relevant here, was this guy who had a very interesting hypothesis, that a lot of the prostate troubles are actually "musculoskeletal" in origin, and muscle imbalance / weakness of the iliopsoas muscles in particular. And that this imbalance affects venous return which "somehow" causes the condition. But he was just a lay person, and the "somehow" was unclear. So this completes that image perfectly. It's interesting that this article mentions the venous insufficiency link, and that veins rely on valves to direct flow, but doesn't mention the muscular link at all.
In any case, this person was saying that in his case, doing lots of iliopsoas stretching and exercises effectively 'fixed' his chronic prostatitis problems. So I've timidly started including a couple of iliopsoas stretching exercises before any workout I do. Anecdotally, I think it helps, but I can't know for sure. But thought I'd mention here in case someone shows interest or can make that link more solid.
PS. found the turkish doctor page (or at least a mirror of it): https://www.oocities.org/iastr/ebroc.htm
I wish I could find that comment about the iliopsoas ... but alas I think it's probably lost in the sands of time now.
UPDATE: Well what do you know. Found it: https://web.archive.org/web/20230203201759/https://prostatit...
(and https://web.archive.org/web/20230127101206/https://prostatit... more generally)