According to Section IX of Ukraine’s 1990 Declaration of State Sovereignty:
The Ukrainian SSR solemnly declares its intention of becoming a permanently neutral state that does not participate in military blocs and adheres to three nuclear free principles: to accept, to produce and to purchase no nuclear weapons.
Joining a mutual defense agreement is not at all holding the gun. Also, NATO didn’t even consider Ukraine until well after Russia invaded.
You have to be pretty deep into the rabbit hole before you can say that Ukraine is the aggressor here.
Not that this conjecture matters, hit me with a soyjack