All the circular features and the light blue but with trailing land is real consistent with volcanic atol formations. Couple that with some notable ridgelines in the middle of the islands and you can do some banger biodiversity a la Hawai'i.

Sporadic lore/myth idea for that middle island between the two big ones: The two islands used to be connected by a narrow land bridge until two rival kingdoms got in a war. The battle there was poised to be the deciding one and both kings planned to burn the other's kingdom and take everything they could. Angered at the bitter fued and careless plans between the greedy kings, a god destroyed both of the armies as they fought and all the land underneath with a terrible force of nature, killing the kings and their armies and preventing the burning of cities and farms that would turn into an eternal fued. All that's left is a giant crater and the land that's no longer connected. (Maybe, in reality, it's a legend perseving the memory of a real explosive erruption ((which would be exceptional on a volcanic island like this that usually has slow erruptions)) and a time of political turmoil. Maybe there really is a god there based on the setting.)

Anyways, this is cool I love worldbuilding like this thank you for sharing : )