In postmodernism, you can’t know reality but you can create a narrative to invent your own reality,
In critical theory, anything that isn’t part of that narrative is subject to deconstruction.
Marxism is basically capitalism bad, labor good.
The blend of these makes up a narative of oppressor, bad and oppressed, good. Then they use identity politics to define these using identities. Deconstruction follows.

I think Marxism is about stealing people's money, supposedly for the poor, but really for politicians pockets. I heard postmodernism is the idea that know one knows anything because prejudice is everywhere. It's also anti-Columbus? Cultural Marxism means so many things.

I consider this caving in more based on “cultural Marxism,” which is a blending of a number of strange ideologies Including Marxism as well as postmodernism.

I see no connection between criticism of Columbus and Marxism.

In a free market those paintings would be moving to a new home in the personal collection of a John Galt, Hank Rearden, or Howard Rourke.
I know some folks who are actively seeking unwanted confederate monuments and statues.