If Russia uses nuclear weapons against a NATO country, MAD will be a factor.
If Russia uses nuclear weapons against a non-NATO non-nuclear-weapon state, there are two possible outcomes.
a) The NPT is discarded and all nations develop nuclear weapons. Eventually there is a bad nuclear war that severely damages the entire human race.
b) The entire world (including China) hammers Russia with sanctions so severe that Russia is destroyed.
I think that when faced with "A" as the only alternative, everyone will choose "B" instead.
That is possible only if it is a non-NATO state that is nuked.
If Russia nukes NATO, then it's nuclear war.
If Russia uses nuclear weapons against a non-nuclear-weapons state, I think the world will hammer Russia with the most severe sanctions in human history.
The International Criminal Court will also issue an arrest warrant for Putin. If they get their hands on him, he will spend the rest of his life in prison. The arrest warrant against Putin may happen anyway due to the crimes against humanity that have already taken place in Ukraine, but it will happen much faster if Russia uses nuclear weapons.