A war crime's a war crime. Doesn't matter if the Ukrainians did it, or the Russians, or Palestinians or Israelis. Or The UN or USA or NATO or Canadians. The only time a war crime's not a war crime is if it's a terrorist group doing it, because then it's terrorism instead of a war crime.
"Terrorism” and "war crimes” are overlapping categories, and being done by something independently defined as a “terrorist group” isn’t what defines something as “terrorism”, rather doing terrorism is what makes a group a terrorist group.
Terrorist is a fancy word for an enemy combatant that you don't like so much they don't get the POW status.