Yes, within the left-right wing paradigm both extreme ends are considered to become increasingly authoritarian and intolerant in support of their ends. Tankies are communists who defend Stalin and Mao using military violence against their own citizens with the justification that their protest/unrest was endangering the whole communist empire which was in a very real way of course under intense pressure, fighting for its existence against the capitalist world.

This is often represented it a parliamentary style seating layout by the horse shoe shape with the far extremes actually becoming closer to each other at the bottom of the horse shoe. It may seem a bit strange but its a good example I guess of how the left-right paradigm as description of political ideology has limitations and is in the end just an abstract model not a true and complete picture.

https://en.m.wikipedia.org/wiki/Horseshoe_theory#:~:text=In%20popular%20discourse%2C%20the%20horseshoe,a%20horseshoe%20are%20close%20together.

I honestly don't know. Wikipedia describes Marxism as left-wing. It also describes left wing as being for social equality, and right wing as believing there is an inherent natural hierarchy to the world.

So the extreme right is believing one race is better than another (e.g. Nazism).

Maxism-Leninism to me is like saying everyone is equal under comunism, except the dictator or small group running things. So sort of a merge between full socialism and Nazism? I guess politics isn't as straightforward as being able to put everything on a left/right spectrum, and I don't pretend to be an expert. I've learnt more about tankies and nazis the last week than in my whole life to that point.