There are many beaches in Puerto Plata, but only a few are worth visiting. I don't recommend going to small unknown beaches, they tend to be full of garbage.
In my opinion, there are 2 really nice beaches here (we do not visit non-public hotel beaches). Entrance to Playa Costambar is 100 pesos per person. The beach offers umbrellas and sunbeds, at the time of our visit there was garbage piled up near the palm trees, I believe that this does not happen during the tourist season. The sand on the beach is light and very fine, the ocean was clean and the natural parasols with palm trees create a natural Caribbean feeling.
The second beach is the most famous and also the most visited Playa Dorada. Entrance is free. The vast beach offers countless paid sunbeds and umbrellas. There are many restaurants and bars nearby, the beach is clean. The trees on the edge of the beach create a pleasant shade.
Playa Puerto Plata was polluted with plastic trash and algae during the off-season at the time of our visit. However, the view of the statue of Neptune on a nearby islet is worth it. Unfortunately, on this long beach there are river outlets and they are very dirty here. There is a nice restaurant with a view on the beach.
The same applies to other beaches along the coast - Playa Acapulco, Playa Caamacho, Cosita Rica, Playa de Long Beach. None of them pleased us, rather we felt disgusted. Mess everywhere - garbage or natural pollution (grass, algae). Nothing for tourists.