The nuke idea is incredibly unlikely, but amusing to think over.
Any nuke on the ground would have to be some Suitcase nuke, so to speak, nobodys trucking in a random ICBM warhead. I find it incredibly unlikely Pakistan would have given them one, if they even had the capability, because the slightest chance that it could be traced back to them would not be worth the interventionist invasion. Same goes for China, nobody would want to let a nuke just loose out their even if they would swear up and down that they're allies.
Which would make the only possible nuke a US nuke. It'd be 100% up the glowies path to have a hidden nuke in Afghanistan in case they needed to start shit, and for it to have gotten left behind in the rapid withdrawal because no way they told anyone about that. And if the Taliban got it, and somehow could set it off...
Well imagine the world stage reaction when a US nuclear device detonates in Kabul, and the Taliban can prove its a US nuke. That would be the *only* situation that the Taliban would 'win' from a nuclear detonation, permanently marking them as the victims, wiping out an entire city of what is, in most cases, collaborators and ex-government that they want dead, and taking a mass of american soldiers with it.
I would sooner bet my life on biden performing a perfect backflip while shredding some Sabaton on a guitar than this even being *possible*, but its fun to speculate on.
But I do have confident the Taliban are going to start executing collaborators on the 1st. They're gonna try to avoid foreigners, sure, but its gonna be a slaughter otherwise, and they're gonna be daring the world to do something. Nobody wants to reinvade Afghanistan (Except the warhawks , I guess) and its going to be extremely hard to get public support for such a move if the people dying aren't your citizens. There will be a lot of handwringing and condemnations, but I don't think anyones gonna be willing to throw fire and steel at the issue if its sufficiently 'internal'.