Practically, anyone with access to the Baltic Sea, boats, scuba equipment, underwater explosives could do it, but they couldn't do it undetected. This area is under surveillance from Sweden and Denmark.
If you want to do it undetected you need to do it completely underwater, including ingress and egress, and that absolutely limits the potential actors.
Another issue with game dev for games that release on PC is that devs are usually on very high-end machines. NVMe RAIDs, 3080's, etc. Great for productivity, but there's very little dog fooding on low-spec machines.
If you want to do it undetected you need to do it completely underwater, including ingress and egress, and that absolutely limits the potential actors.