Found on 4chan earlier, Animal Crossing: New Horizons Summer Update Leak

Diving returns along with 40 total deep sea creatures to catch

The museum updates with a room to display Gyroids dug you, The Roost Café is back, and the Art exhibit returns

The aquarium in the museum gets an update, adding a new room for the creatures caught while diving

Phineas makes his return for the summer solstice event

That’s all I saw in the “leak”. It sounds interesting though, but I doubt it’s real