A tactical nuclear strike against Ukraine by Russia is generally pointless from all sides. Putin doesn't really care about the Russian-speaking population of Ukraine, who will suffer from its use on the front lines in Ukraine. Now, "liberating" the settlements in the Donbass, the Russian troops are deliberately destroying them almost completely so much that it is simply impossible to restore them, and the Russian-speaking civilian population is dying there in the first place. In order to fight further under conditions of nuclear destruction, Russian troops will need to have special protection, and there are very big problems in them and with conventional equipment.

Attacking the western part of Ukraine is like attacking NATO countries, since the radioactive contamination will spread to them as well. And Putin has already been unequivocally warned that they will strike back not only at Russia, but also personally at Putin in his bunker.

In addition, militarily, a tactical nuclear strike will not solve anything militarily. Ukraine will continue to defend itself under any conditions. But it will become clear to the world that Putin's Russia will need to be destroyed and the impending threat eliminated.