True, you can launch one nuke or tactical nukes and keep threatening with the rest. But there's no going back from such irresponsible act and suddenly even the neutrals would become your enemies.
There's no real payoff to such an act and all you get is downsides. Countries historically only thought about using nukes (and I mean Israel) when their backs were against the wall and their country was about to suffer a devastating defeat threatening its existence. That would be if NATO armored columns raced towards Russia's major cities and the Russian army was in disarray.
The Russians may be soundly defeated by a NATO intervention in Ukraine with clear statements from NATO that's all they wanted to do, and Russia would not launch even by their own criteria of nuke use.
There's also the
madman act theory about Putin which explains his behavior.
Putin, change my mind.