Fascism is by definition ultra right-wing. It is fundamentally opposed to Marxism and any ideological movement that was birthed from it (communism, anarchism etc.)

Some may argue that Stalin’s reign in the Soviet Union was aesthetically (meaning it appeared to be) similar to fascist dictatorships in that it was a one-party state, functioned on legitimacy derived from a popular base and was opposed to economic liberalism. Beyond superficial appearances, they are diametrically opposed to one another on an ideological basis. The basis for the Russian Revolution and the Soviet Union that it birthed was the proletarian struggle against the bourgeoisie (working class struggling to achieve a dictatorship that served their needs by suppressing the capitalist class and the structures that support their hegemony). The goal of the socialist project was to rapidly industrialize the economy and create wide-spanning social programs that benefitted the workers - from socialized housing to healthcare to education. Stalin’s goal was to realize this all around the world so that the revolution could be safeguarded against counterrevolutionary elements.

Fascist states are bolstered by an idea of a national myth that typically manifests as racial or ethnic purity of one specific group of people and the subsequent “othering” of everyone else. Their populism is derived not from a proletarian base, but typically on these racial or ethnic lines. This coincided with a rejection of social welfare and of programs to benefit the masses as they felt it to encourage weakness, which would begin to dismantle the credibility of the concept of the “master race”. They are also deeply isolationist. Fascist thought doesn’t promote one specific economic identity over another - their fundamental aim is to build a strong state. In this regard, they have a complex relationship with capitalism because they don’t believe in the validity of the free market but they also firmly believe in private property and the profit motive.