But is the objective to destroy the city? I don't think Putin wants to level Kyiv, he WANTS that city intact and working, just working for him. So tactical nukes are for massed troop concentrations, airfields, hardened fortifications, ports, stuff like that. With the advent of smart munitions the need to either carpet bomb an area or hit it with a nuke has gone WAAAAY down, not that Russia seems to have a lot of that smart munitions either. You could set off quite a few lower yield nucular weapons in an area the size of Texas/Ukraine and it wouldn't impact the area much TBH.
High yield ballistic missiles and the like are for MAD, they have little to no use in actual warfare outside of a possible first strike to take out another nations entire strike capability (missile fields, airfields, political centers, etc) but the ballistic missile sub fleet renders that capability moot since you can't possibly get all the subs on patrol (well, at least not a fleet the size of the US).
In an era with instant communications, I think tactical nukes are actually MORE likely to be used, because the user can broadcast their intent and the deployment in real time so no one freaks out about the launch and detonation to cascade into a global nuclear war. So they become an area denial weapon or a known threat to a specific response (you cross this river in force and you can expect a 10KT nuke). Such an exchange would be locally damaging but for the rest of us it's just another chernobyl/fukushima type event.