"Foucault’s ideas gave rise in the 1970s and ’80s to philosophical postmodernism, a movement characterized by broad epistemological skepticism and ethical subjectivism, a general suspicion of reason, and an acute sensitivity to the role of ideology in asserting and maintaining political and economic power. Postmodernists attacked the attempt by Enlightenment philosophers and others to discover allegedly objective moral values that could serve as a standard for assessing different political systems or for measuring political progress from one historical period to another. According to Jean-François Lyotard (1924–98), for example, this project represents a secular faith that must be abandoned. In La Condition postmoderne (1979; The Postmodern Condition) and other writings, Lyotard declared his suspicion of what he called “grand narratives”—putatively rational, overarching accounts, such as Marxism and liberalism, of how the world is or ought to be. He asserted that political conflicts in contemporary societies reflect the clash of incommensurable values and perspectives and are therefore not rationally decidable."

https://www.britannica.com/topic/political-philosophy/Foucau...

Someone should just stick a fork in the term "postmodern" and finally declare it dead. The above meaning I largely agree with, as would Hume. Of course people can have different values, and of course people with different values, faced with the same facts, might come up with different normative conclusions of what should be done about it.

But that's a far cry from how postmodernism is often decried, as something that professes no objective truth at all, or as a bunch of lazy moral relativism, where the value itself changes depending on circumstance.

So you can easily have two people fighting about postmodernism that might even largely agree with each other; that they dislike moral relativism. But one would attack post-modernism, and the other would defend it, neither really quite clear what they are actually talking about. Which seems to be another definition of postmodernism itself.

Anyway. :) Back to your original question. Given the absence of actual moral facts (which I take as axiomatic), I think the answer is limited to some public decision process that decides which moral values are in force, along with an effective way to re-decide frequently in a way that avoids the problems of becoming insular and self-reinforcing.