What exactly did he do? Agree that Capitalism is evil?
Actually no, and as you won’t investigate it yourself I will give you the ‘Cliff’s Notes’. He shamed Castro. He presented him with a book and a CD set containing a collection of homilies from a Cuban priest. Big deal you say. Well, this Cuban priest was one of Fidel Castro’s teachers. He talked about how good he was as a student and that he had high hopes for him. Subsequently, after the revolution, this priest was forced into exile with many of the other priests ministering to the Cuban people. He ended up in Florida with many other Cuban refugees with nothing and had to start their lives over. This priest travelled around Florida, connecting with his Cuban parishoners, checking on them and to some extent reuniting them in Florida.
The gift was some good old fashioned Catholic guilt to Castro about a young priest that treated Castro as his own son (probably better than his family treated him) and in return he was forced to flee Cuba in exile. It was also a small offering in hopes that the gift might trigger a shot at redemption for Castro - for a repentance and reconciliation.
You can go on about Marxism, but you would show you have not invested much thought into Pope Francis’ background. He spent many many years and faced threats and persecution for fighting and preaching against liberation theology and socialism in South America.