For Cuba -> https://dialecticalartist.wordpress.com/wp-content/uploads/2021/03/cuba-and-its-neighbours-democracy-in-motion-by-arnold-august-z-lib.org_.pdf

For China, there are plenty of books and sources that talk about how the National People's Congress work but I won't recommend any because I have yet to read my long waiting list of books jaja 😅. Maybe, in AskLemmygrad, a comrade could recommend you a good book about it.

Same case for Vietnam. I don't have sources at this moment about their democracy.