The largest nuclear weapon ever tested was the Tsar Bomba in 1961, by the Soviets, at 50 Megatons (MT). Theoretically, they could have doubled it to 100 MT, but did not test that version.
There is no more Tsar Bomba. Making another would violate numerous nuclear arms treaties.
The largest nuke the Russians have currently ready for delivery is 10 MT.
That may be, but Putin’s spokesman is quoted here as saying up to 100 megatons.
“There’s no way of stopping this underwater drone. The warhead on it has a yield of up to 100 megatonnes.”
https://www.irishmirror.ie/news/irish-news/vladimir-putins-ireland-nuclear-threat-26855413
And the USA stopped all biological warfare research because it would violate some treaties.
And Bruce Jenner could never transition cause that would violate his Wheaties