I would question the proposition that postmodernism paved the way for the current era of post truth. My understanding is that modernists believed they were enlightened through technology and discovery and believed they had hit on fundamental truths which they put forward as facts. They then used these facts to fix humanity’s problems. WWI pretty well destroyed that idea and gave rise to such movements as dada in art, where nothing made sense.

This was important so that we could not be dictated to by mathematicians, scientists and economists. Postmodernism taught us to question everything in order to use empirical facts as tools rather than weapons. Facts are not truth. They are the evidence, not the definer of truth. The modern phenomenon of situational truth has more connection with liberalism and libertarianism. Liberals effectively sacrifice universal truth on the alter of self determination while libertarians abuse it to rob lesser individuals of self determination.

Society doesn’t flourish when truth is personalised. It flourishes when everyone is educated in fundamental truths and given the agency to apply it to themselves both in thought and action.