They are so many differences between fascism and Leninism. The end goal of communism is a classless stateless society, Whereas fascism aims for a heavily stratified, Society ruled by a powerful totalitarian state. Just because authoritarian regimes tend to violate people rights, Doesn't mean that the left and right somehow wrap around to similarity.
The Horseshoe theory, which posits that the political ideologies on both sides of the spectrum get closer to each other the further they get towards the extremes, is a valid and accurate theory, with evidence to support it. Throughout history, particularly the 20th century, both extremities have had a tendency to lean into despotism and tyranny, usually fascism on the right, and communism on the left, with fairly similar policies in place, such as restrictions on freedoms of speech.
This can also be seen in some modern day issues, such as globalism, which both the far left and far right have been known to rally against.
THe nazis and communists are very similar but on the opposite sides of the spectrum they both want to initiate force on people and if your ideology initiates force on others it is not a good one that is why libertarianism is the greatest and why the horseshoe theory is correct.