The EU as a whole has over 1.5 million active-duty military personnel, and much more modern and effective air forces. Not to summon Peter Zeihan's spirit, but Russia is on a downward slope in terms of eligible men. And that's ignoring that they can't even defeat Ukraine.
And more importantly, Putin doesn't have the balls to truly go after NATO, even with American sitting on the sideline, since England and France have serious nuclear capabilities that he would not risk.
But here's my thing, putting aside the nuclear issue - if Putin had manpower to spare, we would see it. He literally emptied the prisons, brought in Russian PMCs, brought in a shitload of North Koreans, brought in Africans and Indians that were tricked, and here we are in 2025, the Ukrainians are hitting factories and refineries a thousand kilometers deep into Russia, Muscovites have heard air raid sirens and seen explosions in the distance, the Russians are moving at a snail's pace in Ukraine and taking losses over small amounts of land that they can't afford in the long run, and some of those "gains" they claim, are then reversed by the Ukrainians, and/or are faked.
He's got 700,000 men committed to Ukraine. He would need several times that to try and invade NATO proper when you take into account that his logistics chain would stretch out very rapidly through enemy territory. Right now, his local logistics chain is only under serious threat for the last few dozen miles (from the Russian border to wherever in Ukraine). Stretch that out from the Russian border through Ukraine or Belarus (forces in Belarus would quickly find themselves under NATO attack) and it gets into hundreds of miles, and with rails being hit almost immediately by NATO air/missiles, he'd have to try it by trucks, which he doesn't have a lot of these days.
I firmly believe that if he had even 100,000 or even just 50,000 troops to spare, we would see them being thrown into Donbas or another area to gain control and make his case for claiming that area through "negotiations". I think that's why we are seeing those mobilization orders and building of internal security facilities/groups - he's gotta tap into Moscow and St. Petersburg, and that's going to tie up troops within Russia keeping those cities under control.