If we understand “Leftism” to be about a relationship to the means of production - namely one in which the workers/plroletarian class owns the means of production - then the USSR certainly was socialist/leftist to a significant degree.

Since leftism is about that relationship to the means of production, that also means that a government can be both Leftist and Authoritarian. We can discuss to what degree an ideal leftist government should be “authoritarian”, but that is less a conversation about the economic aspects of leftist political ideology and more about the political philosophy around personal freedoms, freedom of speech, etc. - none of which are completely cut & dry.

One could easily argue that some degree of “authoritarianism” is necessary to protect greater freedoms at the expense of lesser ones - that could be a coherent pro personal freedom and pro authoritarian argument. One could also argue that the anarchist conception of personal freedom is doomed to fail without an “authoritarian” power hierarchy to protect those freedoms. All I’m saying is the question of to what degree the power of the state should be limited is by no means answered.