NATO could certainly rollover the Russian army in a conventional war, but that was just as true before the Ukrainian war. The idea that Russia is/was a serious threat is a convenient fiction: It helps maintain Russia's image as a superpower, and it provides a justification for the existence of NATO and the associated military industrial complex that supports it.

What is true however, is that Russia does possess a huge arsenal of nuclear and other weapons:

https://en.wikipedia.org/wiki/Russia_and_weapons_of_mass_des...

Despite Putin's posturing, Russia's never going to risk deploying them in a conflict with Ukraine. But in an actual war between NATO/Europe and Russia, with the regime facing an existential threat, then there's a very good chance they would. But even before it got to that point, the nature of the conflict itself would make nuclear escalation very likely. Both sides would be firing huge numbers of missiles, attempting to gain air superiority by wiping out the other's own missile launchers, radar bases, etc. With that many missiles flying, and stressed people and automated systems making split-second decisions, it's very likely that an error or miscalculation would result in an accidental nuclear strike, at which point it would be impossible to put the genie back in the bottle.