Post-truth is a concept, or an anxiety
An old version of the Wikipedia entry on post-truth included a description for post-truth as “the disappearance of shared objective standards for truth”, though I can’t find the original source of this statement anymore. I liked this definition, since it emphasizes a social constructivist view
Rhetoric around post-truth was at an all-time high with Tr*mp’s presidency, so much so that “post-truth” was Oxford’s 2016 Word of the Year. Despite this, Yuval Harari has posited that humans are a post-truth species
Truth and power can travel together only so far. If you want power, at some point you will have to spread fictions. If you want to know the truth about the world, at some point you will have to renounce power.
While this is compelling on its own, I’d add that we see this even in fields as cut and dry as math, where entire branches of mathematics topple as soon as you reject a single axiom. The idea of “truth” here is key.