True communism in a country is impossible.
You can have socialism, or anarchy, which we’ve seen before, but communism cannot function in one country alone, unless said country is completely and absolutely self reliant.
A major part of communism is internationalism, which is why socialist countries had the Comintern. (Communist International). Besides a political/social system, communism has a strong basis as an economic system. You can’t apply communist economic system principles to the capitalist market.
To my knowledge, no existing country is self reliant to the point that they can completely cut off trade with the rest of the world. USSR didn’t do it, China didn’t do it and they were the two biggest countries at the time.
That, of course is all a very surface level ELI5, and if you want to ask something more specific or in depth, feel free to.
In feel like you make it complicated to arrive at your conclusion here. Communism, as described by Marx and Engels and to some degree Lenin, is something very specific that covers most aspects of the society. Political, social and economic. Marx himself wrote books upon books on the economy of a socialist, communist system.
It is not an abstract “I don’t like capitalism so let’s try something different” approach. And yes, many have tried to adapt it, as you mentioned which is why those different approaches carry a different name ‘anarchist communism’ in your example. Because they are different enough from flat out communism.