I think there are two components to nofap, there are effects of semen loss and effects of orgasm.
To me, semen loss is the clear physical harm, you can feel your brain becomes foggy, might forget things, heart beats harder, lose strength for exercise, you have to eat some protein to make up for the loss, can get stomach pains from digesting to create semen, and so on.
I have doubts porn is really that physically harmful, because it is indistinguishable from looking at an actual wife you marry, but it will likely have psychological negative effects of shame and guilt.
As for orgasms themselves, they seem possible without losing semen or with minimal loss and if hypothetically you lost no semen, these might be physically healthy (but again susceptible to the problem of psychological and spiritual loss). It might reduce tension which would have been used creatively or overload your brain's chemistry.
I'm ultimately attempting nofap and noporn for spiritual reasons and retaining semen feels like a clear and obvious physically beneficial action so that's something to avoid even during relapses.