Some experts have said he feels he has nothing to lose at this point so he will go all in.
This is the problem. Everyone saying it's not rational and even suicide to attack NATO is correct.
Everyone also said it was totally irrational to attack Ukraine in the first place and they'd never do it yet here we are.
Russia is not a rational actor at this point, so we have to assume anything should be on the table. That doesn't mean we should escalate but we should be prepared for all scenarios.
Russia reinforced their right to use nukes today, if they're threatened, even by conventional weaponry.
So here's some food for thought. Say Russia does use chemical weapons or a tactical nuke in Ukraine or is bold enough to directly strike a NATO country.
If NATO gets involved I find it hard to believe they will merely fight to restore Ukraine's territorial integrity, and should they manage that allow Putin to remain in power. It will be wholesale regime change in Moscow or nothing. How would China feel about having a Russia sized, Western puppet up against their border?
China got involved in the Korean war because they didn't want the entirety of the Korean peninsula to be controlled by the US. Should NATO get dragged into this and end up with Moscow being directly threatened, there is certainly a possibility that China gets involved, so the idea that Russia would be a cakewalk for NATO is fanciful imo.
Offensive wars are harder to fight than defensive ones. A war against NATO would likely galvanize the Russian people and military. Russia has the worlds largest stockpile of nukes, and there's a non zero chance China comes to the Russian defence in that scenario.
We should be trying to avoid a conflict between Russia and NATO at all costs, but the idea that Russia attacking NATO is ludicrous and would never happen is most certainly wrong. I have no doubt Russia would try it under the right circumstances.