This year in September we spent a few days on island Lopud.
It's an hour ferry ride away from Dubrovnik. It's a nice small island with just around 200-300 inhabitants but maybe 2x more tourists. In the main part of the island is near the harbour. There are some churches, some shops, hotels and restaurants on the promenade. There are many private accomodation on the island, we also booked in one of these - with nice view to the sea and to the city.
From the harbour there are good signage how to get to the naturist beach, it's about 30 min walk. Tha naturist beach is the left part of Sunj beach.
This is famous because this is one of Croatia's few sandy beaches. Unfortunately very touristy. Full of sun umbrellas and sun beds to rent and expensive bars. And at the very left side there is a small designated nudist beach. Unfortunately the most dirty part of the beach (I guess the wind brings the rubbish to this edge). But the water was nice. When we were there there were very few people there.
There is another naturist "beach" on the island, on the island's closest part to the mainland, also about 30 min walk from the center. But it's not really a beach but some rocks where it was very difficult to get into the water. Bring swimming shoes! Also very few people. But the water was very nice there. Here there are no services nor bars, here you need to take your own food/drink if you want to spend more hours there.
It was nice to visit this island for a short time but I think it is not a very good tip for a naturist holiday.