Soldiers of the Group 13 special forces unit of the Defence Intelligence of Ukraine destroyed the guided-missile corvette Ivanovets, part of Russia’s Black Sea Fleet, on the night of 31 January-1 February 2024.
Not a huge one. The thing is, they can't move their navy to the Black Sea so they're limited to what they already have there. Of those ships they have lost quite a few, but outside the Black Sea that l they still have a substantial navy.
I think they also can't leave without permission either. I say this because I'm not sure if Russia would even want more ships to be there with how things are going with their Black Sea fleet. lol
Because of Russia's vast geography and relatively limited waterway access, it's better to think of their different fleets almost as individual smaller navies.
Especially in the context of the Black Sea fleet and Turkey's ability to restrict access of military vessels through Bosporus and Dardanelles Straits because of the Montreux Convention.
So to answer your question under that more narrow scope, I believe it's roughly 20% of the Black Sea fleet has been destroyed.