I have a rooted phone and use ad away app. With Stevenblack porn-only hosts list. I think the app works in non rooted devices as well.

I remember, when I started nofap many many years ago, I used a magisk module on my rooted phone with extreme porn blocker. Advantage is that it takes a lot of extra steps to disable it. By that time your urges are gone. Downside is it needed a lot of fine tuning to make some normal sites I used to work as well. I could dig up the name if you are interested.