So lets clear something up: the two attributes objective/subjective and universal/relative are logically distinct. You can can have objective relativism ("What is moral is the law and the law varies from place to place.") and subjective universalism ("What is moral is just our opinions, but we all have the same opinions").

a fact of reality able to be investigated by science that is independent/prior to any of the mind's later acquisition of knowledge/content", versus "something that is not an independent/prior fact of reality, but rather some later invention of the mind".

The attribute "objective" or "subjective" in meta-ethics refers to the status of moral judgments themselves not descriptive facts about what moral judgments people actually make or the causal/mental facts that lead people to make them. Of course it is the case that people make moral judgments, that we can observe those judgments and can learn something about the brains that make them. No one here is denying that there are objective facts about moral psychology. The entire question is about the status of the moral judgments themselves. What makes it true when I say "Murder is immoral"? If your answer references my mind your answer is subjectivist, if your answer is "nothing" than you are a non-cognitivist or an error theorist. All those camps are anti-realist camps. Objectivist answers include "the Categorical Imperative" and "immorality supervenes on human suffering".