Not sure why you are so convinced of that.
Well it is quite simple. Appeasement never ever works. History will show and tell you that.
Putin and other autocrats like him only understand one thing and that is strength.
Every day over the past 1,000 days since Russia illegally invaded Ukraine, we have heard Putin and his cronies bellicose rhetoric. Indeed on the night of the invasion, he spouted the same rubbish.
Putin may be many things, but he is not suicidal. Launching even a tactical battlefield low yield nuke, would see such a conventional response from NATO countries, Russia will no longer have an army in occupied Ukraine after 24 hours.
Furthermore Putin would have to live forever underground in one of his bunkers. Because, by launching a nuclear strike as soon as he reappeared, a hell fire missile would no doubt zoom in on him ASAP.
You are also forgetting the other players, such as China and India. President Xi would no way allow Putin to launch a nuclear weapon.
The thing is though, by changing their doctrine and people like Markov going on the main stream media, foretelling doom and gloom the end is nigh stuff, you, yes you and everyone in this thread that believes we are on the precipice of global armageddon, are drinking Putin's Kool Aid.
Supply weapons to Ukraine - Red Line
Supply Tanks to Ukraine - Red Line
Strike the illegally annexed territories of Ukraine - Red Line
Hit the Kersch Bridge - Red Line
Supply F16's - Red Line
There is a pattern here, shame you cannot see it.