Being a member of NATO does not preclude member states from making individual decisions to provide military assistance to other countries. That's exactly what is going on in Ukraine. Article V has not been invoked, and to the extent some of the individual countries that make up NATO have chosen to help Ukraine on their own, that's up to them. Likewise, NATO member states like Hungary who have chosen not to provide assistance are not in breach of their NATO obligations because Ukraine is not a NATO operation.
There are dozens of examples over the decades of NATO member states providing assistance to nations outside the umbrella of NATO. Hell, in Kuwait, we saw NATO member states providing virtually all of the combat troops, aircraft, and ships themselves in a non-NATO operation.
And Russia in the costume of the Soviet Union, while a member of the Warsaw Pact, also provided military assistance to nations outside the umbrella of the Warsaw Pact.