Yeah but thats just the opium masses crap. Christian Socialism is a thing. Case in point Ceasar Chavez and the sheer amount of work he did for the labour movements. The two systems are compatible.

Marx’s view of communism doesn’t inherently ban religion. His view of religion was that it was a tool by the ruling classes to maintain the status quo against the oppressed, and that under communism religion wouldn’t hold any political power because, by his words, the conditions that allowed religion to hold political power such as inequality wouldn’t be present anymore. But he didn’t call for the abolition of religion or that religion couldn’t exist at all in a communist society, that was more of a Marxist-Leninist way of thinking.

Marx literally wrote against enforced atheism in "the Jewish question"(a very unfortunate name in hindsight) which was a defense of Jewish communists keeping their religious and cultural identity.

I'm pretty sure he was involved with the liberation theology movements in Argentina before the previous pope clamped down on it (in his capacity as a cardinal)

Highly unlikely. Hell, many so-called "Marxists" have not.