I will not be surprised if nukes are used or even already have been used but IMO nukes are a lot less offensively useful in the precision guidance era than people assume they are late in a long war when high end materiel is running out the calculation might change, but I don't think russia gets much out of using nukes in ukraine. they can already hit targets with precision and it's a rare target that can't be busted with a large conventional weapon but can be busted with a nuke of course if you just want to kill as many people as possible then sure nukes are great for that