What does NATO article 5 have to do with Ukraine?
What would come next after Ukraine may be the Baltic states or Poland.
According to your YouTube sources? NATO has nothing to do with Ukraine. NATO countries can defend themselves if one of those countries actually are being attacked. That happened in 9/11 and NATO countries supporting militarily the US wars that preceded.
They have no such obligation towards Ukraine.
There is if you ever want to negotiate a nuclear arms-control deal again. None of this would be an issue if Ukraine had kept their nukes.