Fascist is more than just authoritarian, there’s a lot of other components (fetishization of the military, an obsession with returning to the “good old days”, portraying scapegoats as simultaneously unbeatably strong and pathetically weak, etc)
The USSR was authoritarian, but not fascist.
EDIT: To clarify, I’m no fan of the USSR and their actions to put it mildly, but we shouldn’t dilute the word fascist by making it a synonym for authoritarianism.