I think most people would not agree that "private freedom of association" has ended in the US. There are protected classes, you're not allowed to discriminate against someone for their existence as a member of a protected class, but there are definitely still plenty of ways in which I'm allowed to bar people as I see fit (in my locale, "no Biden/Trump supporters allowed" would be legal).

Are you referring to the Civil Rights Act? freedom of association is a construct made up by modern nation states and people.

It was never truly freedom. Classes, hierarchy, power, in the modern world order led by the US and western Europe. Fred Hampton was murdered by the racist capitalist government after the CRA passed. Before one can get to any sort of freedoms, one must not be killed by the same state bestowing such freedoms.