(Layperson here.)

Scientifically, no. There's no reproducible evidence that any diet or supplement affects the spread of prostate cancer. You'll find very-confident personal anecdotes here in the forum, and you can take them for what they're worth — a diet with X or without Y might have made a person feel better purely by power of suggestion, or because it helped with something different (irritable bowel, reflux, lactose intolerance, diabetes, etc) that the person wasn't aware of.

That said, a normal healthy diet is always a good idea, with or without cancer — just follow your grandma's rule of covering at least 50% of your plate with vegetables, 25% with a starch (potato, rice, etc) and 25% with a higher-protein source (meat, tempeh, beans, etc). Cancer's complicated; eating doesn't have to be.

Also, it's worth considering adjusting your portions so that you're eating just until you're no longer hungry instead of eating until you're stuffed; you might find you have more energy that way (obviously, this doesn't apply if you're getting chemo or experiencing another medical condition that makes it hard to eat and you're at risk of undernourishment; in that case, don't slap portion limits on yourself).

If you get radiation or surgery to your prostate, you might experience urinary-tract irritation or incontinence. In that case, you might want to reduce potential urinary-tract irritants for a while, like caffeine, alcohol, carbonated beverages, and spicy food, just until the irritation stops. I had to cut down to one cup of tea/day for a while in summer 2023 due to radiation cystitis (bladder damage), which was rough, but I no longer need to limit it.