Nazism and communism are completely different concepts.
… different totalitarian concepts.
Wrong. While a large number of communist labelled regimes were in fact totalitarian regimes (whether they actually were communist is another debate), totalitarianism is not inherent to communism (and it can be argued that a democratic foundation is necessary for communism or that communism is the democratisation of labour). However, fascism is characterised by (among others) an extreme form of authoritarianism (i.e. totalitarianism) that is structured after the Führerprinzip.
Lots of things can be argued in academics. The largest communist experiments have been totalitarian. The idea that democracy is a core component to a communist society is now more commonly referred to as democratic socialism.
Democratic socialism isn’t socialism, except with democracy lmao.