What evidence is there that Mao’s Great Leap Forward was a failure?

Evidence of the failure that the Great Leap Forward was were the large-scale poverty, economy on the verge of bankruptcy, and famine leading to millions of deaths.

Explanation:

The Great Leap Forward was a set of actions undertaken by Mao in order to try and improve the country's position in the world, but also to keep the people's belif and support. While at least one aspect of this was with good intention (the other one not), in reality, it was a disaster. Not just that it was a disaster, but Mao was managing to successfully cover it up in the most important parts of the country.

The Great Leap Forward led to terrible economic conditions in the country. The population was already very poor in general, but the very bad planning resulted in such big failures, especially in the agricultural sector, that a very large portion of the population was experiencing famine, and not just that but died from hunger. The people that were producing the food were actually stripped of it so that it can be delivered to the people in the cities, thus the basic labor force died from hunger, opening up a problem for the coming years where there wasn't enough people to work on the fields.