Marxism opposes materialism because it is deem to be a key engine in class warfare

Dialectical Materialism is literally a product of Marx and Engels. Granted they didn’t call it that, but they very much called it Materialism.

And everyone who took after M&E used D.M. Lenin wrote Materialism and Empirio-criticism. Stalin wrote Dialectical and Historical Materialism. Mao wrote On contradiction. George Pulitzer, a teacher at the Workers’ University (which taught marxism), had a student write up notes from his class into a book: https://en.prolewiki.org/wiki/Library:Elementary_principles_of_philosophy