Putin has wisely not used tactical nukes on the Ukraine as this could lead to a nuclear war nobody wants. However, the Wagner group marching toward Moscow is entirely different. This truly is an internal matter of Russia. Putin might use nukes on Wagner?
Maybe. I have wondered about that. He may not have the ability to do so.
It would have to be tactical nukes. Who controls them, and are there any available for his use, in the right place?
He has air assets available, and they probably have some tactical nukes. But nuking Russians on Russian soil seems pretty risky...
Collateral damage on Russia, especially in the heartland where PR matters most.