Only if they think they will gain. They can't possibly think a strategic exchange is desirable, so what would they gain from using them against Ukraine? Any use in Ukraine is very likely to trigger a NATO conventional response that would definitely not be in Russia's interests. Nukes against a NATO power would get a comparable Russian site nuked and probably lead to a strategic exchange, so that's out as well.
It is called a line in the sand. Russia has stated numerous times its war with the Ukraine is existential. That means we will go to any length to win. The logic may be flawed and silly but it is clearly stated. Theater nukes will prove the Russians really do mean business . Next up will be targeted nuclear destruction of some major city. (Lwow , that would get Poland’s attention as well) Not Kiev, the Russian nuke doctrine is to leave someone who can either surrender or negotiate an end game. Is there anything in the Ukraine to make any other country to be involved in a war now over the nuclear threshold. I would argue absolutely no. But politicians combine a remarkable capacity for cowardice, panic, and mindless risk taking.