Uhh, that's completely illogical. Yes, Russia broke international law by invading a country. That's true. That does not give the USA the right to attack Russian territory. That's not actually how international law works.

There are lots of reasons Ukraine isn't part of NATO. The first one is that Ukraine made a political commitment with Russia to remain neutral. The second is that Russia made it clear that Ukrainian neutrality was to be respected by NATO allies. The third is that the USA knew how dangerous it would be to bring Ukraine in so they worked on every other former Soviet Republic first. The fourth is that the NATO allies don't all agree on bringing Ukraine in. And the fifth is that NATO policy forbids admitting a country in an active border dispute.

You can say that nukes make it WW3, but that's just vibes. World war is when a war between 2 countries expands to include more countries. Right now, the war is between Russia and Ukraine. If the USA gets involved, then the USA is escalating to world wars. Your vibes are not the standard.