Dolphins

On the Java Edition, you break them instead, as you can break them in survival mode, which aligns with the intended behavior as per MC-102908, although in my opinion, they shouldn't be breakable.

This behavior isn't considered a bug. There's no reason why you shouldn't be able to mine blocks while riding a boat. The entity you're riding is consistently untargetable, allowing you to interact with blocks or entities by aiming through it.