There is no link between COVID vaccines and prostate cancer. OTOH, there *is* a possible link between repeated infection/inflammation and cancer, so anything you do to reduce the risk of major respiratory ailments — including keeping your vaccinations up to date — may reduce slightly your risk of respiratory-system cancers. More importantly, getting vaccinated also protects the people you come in contact with, including the elderly, the immunocompromised, babies too young for vaccinations, or people who can't get vaccinated for medical reasons. Win-win.

An Omega-3 supplement like fish or krill oil doesn't help your prostate cancer directly, but it's hugely beneficial for counteracting some of the side-effects of hormone therapy, including the cardiovascular risks. There's probably no good reason not to take one.

Vegetarians and vegans can get their Omega-3 from flax-seed or algae oil. I take this supplement, from Kelowna, British Columbia:
https://freshfield.life/products/vegan-omega-3-dha-dpa-ca