Yikes. Some truths are more truthful than others.
Yes. Within science, Popper, Kuhn and Lakatos all wrestled with how poor scientific programs/paradigms/central theories are replaced with better ones.
With respect to science vs, say, corporate funded media campaigns or religious ideologies, science does a better job describing and predicting the natural world.
Who decides this "truth"?
Within science, it is generally done in the consensus building institutions such as the various national and international scientific academies. They are generally well positioned to synthesize results across a given field.
Among the general public, the sad horrifying reality is that everybody individually will decide whether or not to accept the consensus of institutionalized science. Ironically, science itself (cognitive psychology, particularly) tells us that a significant % of the human population is biased to put more faith in their conservative religious or political ideologies than in science - hence the mask wars and lack of public embrace of global warming. I've concluded that the human brain isn't collectively fit enough to survive the extinction epoch that it has manufactured. I've wept enough and shed my last tear in this direction and my compassion is all used up.
And postmodernism does not follow science when it does not fit their narrative (gender identify, for instance).
From Scientific American:
https://www.scientificamerican.com/article/the-unfortunate-fallout-of-campus-postmodernism/
Shermer, the author, is a former Christian fundamentalist and his views on scientific epistemology are what I call "scientific fundamentalist". His views on post-modern philosophy a) mirror those by other scientific fundamentalist and b) are horribly wrong.
The connective tissue between his Christian fundamentalism and his scientific fundamentalism is that he's thoroughly stuck in the very modern quest of finding dead certainty. He's traded an absolutist religious view for an absolutist scientific view. I have a friend who writes in the science & religion field who could have written the same exact essay and he's just as wrong and just as fundamentalist as Shermer.
IMO, the much more robust view of scientific epistemology a) accepts that all scientific truth is socially constructed through rigorous social processes and b) asserts that this process produces better, more reliable truth claims about the natural world.
IMO, the strength of a post-modern conceptualization of science is that is allows us to recognize and adjust for the social factors that influence science. Phrenology was bad science. Having so much of the US scientific field dancing to the piper of the defense industrial base, big pharma and big agriculture are similarly bad. Shermer (and my friend) want to put science beyond any social critique - which I and other social constructionists won't accept.
But this doesn't mean that science should be dismissed and replaced with Kellyane Conway's "alternative facts". Current scientific consensus is the current best description of the world. If you don't like what the science says, do better science.