The terms "our reality," "complete understanding" and the "scientific approach," need more robust definition. As is, answers to you query will be hit and miss affairs that may fail to fully satisfy (cf the varieties of answers you’ve received already, including my own). Moreover, while all are anti-realists, and claim that the world/reality is constructed, rather than discovered, all the way down (our concepts do not “cut reality at the joints," as they like to say), and hence passionately reject the correspondence theory of truth, there are various brands of postmodernism, each of which posit different alternatives to word-world correspondence.
Derridian PM, for instance, holds that that while there is a signifier [a word/concept], there is no [there is an “absence” of a] signified [a corresponding object in the world]. There is no word-world relationship to speak of, texts refer only to other texts, words to other words, ideas to other ideas, beliefs to other beliefs, concepts to other concepts, etc. Foucaultian PM claims essentially that all knowledge [including scientific knowledge] truth and rationality are chimera, are no more than functions of power, tools of the powerful, the oppressors, as a way of maintaining their power and control over the oppressed. (See, for instance, Frankfurt School critical theory [https://plato.stanford.edu/entries/critical-theory/] etc.).
As a natural scientist, however, it seems to me that the ground upon which the skepticism highlighted in your question is better addressed by coming to terms with the 20th Century notion of post positivism, commonly characterized as:
A metatheoretical stance that critiques and amends positivism. While
positivists believe that the researcher and the researched are
independent of each other, postpositivists accept that theories,
background, knowledge and values of the researcher influence what
This utterly reasonable notion arose within the tradition of Anglophone Analytic, as opposed to Continental [PM's birthplace], philosophy. However, both Postmodernism and Postpositivism are children of the Kantian idea that all knowledge is necessarily mediated, that we have no access to the thing in itself, the noumena [i.e. to unmediated reality], but only to phenoumena [i.e. appearances]. So the salient issue in epistemology and the philosophy of science has essentially come to be whether and to what extent the world/reality constrains what we can say/know about it.
While for Kant our perceptions are mediated by fixed/eternal "Categories" [his pure concepts of mind], the post Kantian Hegelians introduced Historical contingencies that mediate our perceptions of reality/the world. (As an aside, the road to Postmodernism was paved by Hegel's Historicism and Husserl's Phenomenology.) Needless to say, it has all become impossibly complicated.
As I have on numerous occasions here in response to queries of this type, I urge you to peruse intellectual historian, John Zammito’s, A Nice Derangement of Epistemes: Post-Positivism in the Study of Science from Quine to Latour. (https://www.amazon.com/Nice-Derangement-Epistemes-Post-positivism-Science/dp/0226978621), which tracks the 20th Century movement in Anglopone Analytic philosophy from traditional epistemology and philosophy of science (that there is, to a greater or lesser extent a rational basis for theory choice) to the radical constructivism of the sociology of knowledge and of science studies, which have arisen from what Zammito considers to be hyperbolic misreadings of WVO Quine's holism and underdeterminism [of scientific theories], the reasonable when restrained notion of theory ladeness of facts/perceptions [sometimes discussed under the rubric of the "myth of the [unmediated perceptual] given," and Kuhnian incommesurability [of scientific theories], from from his 1962 opus, The Structure of Scientific Revolutions). Or. as he puts it:
“The three hyperbolic dogmas of antiempiricism [which have] dominated
'theory' over the past fifty years of post-positivist thought:
theory-ladenness, underdetermination and incommensurability. None [of
which] is justified in the radical form which alone empowers the
extravagances of postmodernism.
Given your interests and background, you will appreciate this read. And while it may not fully answer the questions you pose, it will contextualize them, provide you with an etiological handle on the issues they raise, and maybe even enable you to answer [resolve or dissolve] them for yourself.