Ukraine could absolutely be fighting a dirtier war than it is. They could be much more aggressive with attacking soft targets in big russian cities, car bombs, shooting up stores, assassinating government figures, blowing up civilian structures. They've already shown a capability and willingness to do this, assassinating Dugin's daughter and some high priority targets here and there over time.

But - unlike the russians, they have allies/supporters who care about moral conduct of a war and an ethical high ground, thus they don't bother with those kinds of attacks at scale. But if Russia were to start using nukes to kill large numbers of Ukrainians in a clear final act of extermination (a Final Solution, if you will) , there would be no reason for them not to fully unleash a terroristic campaign like that, and really make the passive enabling Russian population feel the venom that their government has unleashed.

A tactical nuke is just a big shell - depending on a programmable explosive yield, it might blow up a single building or a few city blocks. Militarily, there isn't a single target that changes the trajectory of the war by being nuked - but politically and strategically, using any level of nuke probably creates way way way more problems for russia than it solves.

Why believe that? Because they clearly didn't use them at points where there were more concentrated Ukrainian defences that might at least at a simple tactical level, have an argument for their use if you turned off your brain and soul and thought like a Russian does, for a minute. They could have used them against any number of fortress belt cities where Ukrainians were (or are still) stubbornly entrenched like Bakhmut, Sieverodonetsk, Avdiivka, Pokrovsk, Mynohrad etc, and expect that the Ukrainians would quickly retreat and reconsider their defensive posture for the next town down the road. But - the central contradiction here for Russia is that they insist Ukraine belongs to them - ergo is their property. Why would you nuke your own property, especially with all the other entanglements it presents. This is a war of land seizure by a mafia state looking to steal wealth and treasure from their neighbour. You can't extract value as quickly from a completely decimated moonscape, plus your reconstruction costs are higher.

They're not going to use nukes of any kind. And China probably would pull all support if they did, which would QUICKLY deindustrialize the Russian army to the point where they'd be using slingshots and sticks on meat assaults in a couple of months.