"Communism failed because it was not sustainable, there were no incentives, no motivation, no other way of ruling but by fear. "

https://monthlyreview.org/2009/05/01/why-socialism/

here is an essay by Albert Einstein titled why socialism, you should read it.

it seems like you can't define communism and you don't understand human motivation. If your only reason for doing a job is to survive and not because you enjoy it you will never give it your all, that's capitalism.

https://simple.wikipedia.org/wiki/Communism

also the only reason the ussr "fell" was because they allowed an opportunist to reform the country towards capitalism. 80% of the people voted to keep the ussr communist, but it turned capitalist due to the influence of the newly created ruling class.
"As far as I know has never been tried at large scale"

how about anarchist Spain and anarchist Ukraine lmao.