There's still stuff that I think that they could have done. If they're trying it, I don't believe that they're doing a very effective job of it.

In World War II, the US's response when it was clear that aircraft were going to be a lot more dangerous to ships than originally-anticipated was to weld AA gun platforms everywhere they possibly could onto the ship, including hanging off the sides. The guns weren't intrinsically any sort of tech wonder, but the more lead they were putting out, the greater the chances of a hit in the time that the aircraft was closing. I've definitely seen video of Ukraine running USV attacks successfully while Russia was shooting at the drones and not hitting them.

In this case, I'd think that they could have put something like autocannon platforms or quad-mount heavy machine gun mounts on the thing or the like. Maybe they aren't integrated with the ship's fire-control system, have to have someone physically go out there, but this doesn't require amazing accuracy so much as throwing more lead downrange.

They could have had patrol boats or some other kind of smaller, less-capable vessel screening the larger ship. That's historically the response that was taken to the introduction of torpedo boats, which historically had a somewhat-similar role to these USVs -- relatively-inexpensive, small vessels that could hit hard enough to take down a much-more-expensive ship. The torpedo boat destroyer, which ultimately became the destroyer, was introduced to fill that role; it wasn't a very large vessel, but it was enough to stop a torpedo boat.

My guess is that it's possible to use laser-guided ATGMs to hit boats. Norway uses TOWs in a man-portable form, IIRC on a tripod launcher, for coastal defense to counter boats. That doesn't require any modification to ships, just sticking someone trained to use them on the ship and some ATGMs.

If the problem is not picking up on the fact that the USV is there until too late -- I didn't see any shooting at the USV this time -- they can increase the number of people on watch and their equipment. I believe I saw a searchlight on one in the past, and they could probably stick more floodlights on the thing.

I mean, that costs something, but they know what ships they're putting in the danger zone, where to put resources, and losing these ships to really inexpensive USVs has to be far more costly to the Russian Navy.