Those weren’t communist
The USSR wasn’t communist, it was in a place in between Capitalism and Socialism(State Capitalism), but then Stalin took over and It became a dictatorship.
China was supposed to be Market Socialism, mixed Capitalism and Socialism, but became capitalist in the early stages and because of globalization it became cheap labor central.
Cuba is actually very democratic, most of the poverty there can be attributed to the US embargo on Cuba.
North Korea is a result of the USSRs imperialism and functions like the USSR, it is a dictatorship.
Vietnam and Laos were also the product of the USSRs imperialism and were immediately attacked by the US.
The Kibbutzes were an oppressive form of ethnic nationalism, which goes against Socialism.
Hitler took over a “Socialist” party, but was not actually Socialist, he abandoned all populist ideals once in power, banned all real Socialist/Communist parties and turned the party into a white nationalist party, which goes against the socialist ideals of equality and internationalism.
Pol Pot was like Hitler, he took over a “Communist” party but wasn’t communist. In fact, he was self-describedly not a Communist. In the Cambodian massacre, the U.S funded KM and bombed 900k innocents.
Venezuela doesn’t even have a socialist constitution or economy.
But this doesn’t mean communism is doomed to fail because of “Human Nature”, almost all attempts have been destroyed due to Capitalist imperialism, low technological and economic starting points, and a bad situation to inherit.
Despite this, places like Rojava, Revolutionary Catalonia, Parts of Chiapas (the Zapatistas), Anarchist Argon and many other places have proven Socialism can work.
The USSR wasn’t communist and a lot of other supposedly communist countries were a product of its imperialism.