It’s not terrorism when it’s a major state actor and they’re not hiding their involvement. That’s just war.

Uhm, no, based on your definition not even the official 9/11 story’s Al-Quaida would be considered terrorists because they supposedly admitted to what they were doing:

FBI’s terrorism definitions:

International terrorism: Violent, criminal acts committed by individuals and/or groups who are inspired by, or associated with, designated foreign terrorist organizations or nations (state-sponsored).

Domestic terrorism: Violent, criminal acts committed by individuals and/or groups to further ideological goals stemming from domestic influences, such as those of a political, religious, social, racial, or environmental nature.

Encyclopedia Britannica:

terrorism, the calculated use of violence to create a general climate of fear in a population and thereby to bring about a particular political objective. Terrorism has been practiced by political organizations with both rightist and leftist objectives, by nationalistic and religious groups, by revolutionaries, and even by state institutions such as armies, intelligence services, and police.

Cambridge:

violent action for political purposes

Al Queda was a non-state actor with state support. You bolded “nations”, but that whole line says “designated foreign terrorist … nations”. The Ukrainians are not trying to instil fear, they’re cutting a major logistical line with military uses.

Devils in the details, as usual.

I also bolded nations (state-sponsored), political organizations, state institutions such as armies and intelligence services.

Exactly for that reason. Ukraine is openly and clandestinely attacking* Russia, most likely with help from Western governments. The goal is to instill fear in the Russian population in order to reduce the russian population’s willingness to support or accept the ongoing SMO/war against Ukraine/NATO expansion.

• I’m not judging, they’re at war.

If the goal were to instill fear in Russian citizens, they'd be attacking Russian citizens.

They are not.

They are attacking a Russian supply line to hamper their offensive efforts.

When you give bad faith actors the benefit of the doubt, you look like a bad faith actor yourself. Stop parroting Russian talking points as if there's a way for Ukraine to have their approval without capitulating.

If the goal were to instill fear in Russian citizens, they’d be attacking Russian citizens

For example, like the Kremlin is bombing Ukrainian apartment buildings and murdering civilians.