Note that cutting the gas aligns with what the West citizen broadly want: Being forced faster than later to get rid of fossil energy. EU leaders certainly didn’t aim to secure the gas supply, they put all their might into sanctioning Russia “even if it costs the gas supply”.

At this point I’m wondering whether Russia knows it and wants to impose any sanction except cutting the gas.

Western citizens to not broadly want that at all. They may say they do not that's conditional on a lot of unstated assumptions, like it not causing electricity to become unaffordable or entirely unavailable. Both of which would be likely consequences of an energy was with Russia. The moment that happens, people sitting in the cold will suddenly remember that Ukraine is a foreign country and they aren't actually at war.

If Russia cuts the undersea cables that's going to be even worse for them.