Learn Mando'a

Maybe this could be used by Mandos on aquatic planets. Though, it doesn’t seem beskar floats, as I found out after watching the scene in The Mandalorian on the fishing boat.

Neat! I bet it could float if you added some sort of ballast tank, like a submarine has for buoyancy. Or hey, why not just say it's repulsors?

Very good!

I would remove the webbing or make them shorter around the index fingers in order for an easier time to fire their weapons. Just a tidbit of advice!

I feel like in the water you usually have your arms up a lot and there is a lot of exposed leg on the sides. Maybe there could be the addition of some sort of kama? Though that would increase drag and perhaps tangle the arms if sinking feet first.

You have to remember that Beskar is dense and heavy as hell (though most Naur'alorse should get around that). Just add a jetpack or some other form of propulsion and you should be able to have them maneuver find underwater though. The flippers don't really do anything then if you have the propulsion system, but shorter should make sure you don't get drag while flying underwater and also help in quick bursts of movement and adjusting position.