Can you please provide links/evidence about the false west propaganda regarding China, Rusia, Cuba and Venezuela?

Generally, you needn't be motivated to disbelieve every bad thing about every non-Western country to maintain some angels/devils narrative of the world.

I have talked with some people from Cuba and Venezuela (expats) that support the west narrative about poverty and mismanagement.

You should listen to people. People in Cuba and Venezuela are hurtin', no doubt. People experiencing poverty don't see the causes of it, oddly enough. Going through poverty doesn't give you insight into that part of the story.

Venezuela was definitely mismanaged, mostly by a lack of diversification outside of oil, and a lack of financial sustainability (blowing their money too quickly).

But I don't get how any of this rebuts the harmful effect of Yanquí sanctions. Problems usually have more than one cause.

I “believe” that Russia is attacking Ukraine for selfish reasons... please prove me wrong.

Russia is an ultra-capitalist regime, no need for leftists to defend it.

I “believe” that... China censors access to foreign information using the Great Firewall, please prove me wrong.

This is a tricky one. My friends in mainland China tell me they surf the web as they want, use VPNs as they want. It seems to be pretty commonly accepted there, like smoking weed in countries where that's illegal but everyone does it.