I remember reading this somewhere years ago. The idea is that Israel will nuke Paris, Berlin, London, etc, in the event that the west cuts off their support and allows it to be defeated by an enemy force.
Is this just a dumbass conspiracy theory, or is there something to it?
I would interpret this as a narrative intended to excuse and explain Europe and the West's behaviors. It's a defense against the idea that they're monstrous colonizers that actually support and agree with Zionism.
It also plays into the "actually those Jews over there control everyone else with tricks and threats" antisemitic canards. These two things work together for Euros and white supremacist liberals.