Putin is not stupid, he will not use nukes but the Swamp politicians, and far, far, far too many journalists are floating that boat to serve their purpose.
They have babbled about, but DO NOT KNOW if Russia has used a Thermobaric bomb but that is the very nasty item I would bet every cent I have on.
The Tu-160 bombers have been converted to be able to carry conventional bombs, and can carry a load of up to 100,000 pounds.
One or two of them, dropping a full load of said bomb would leave miles of rotting corpses.