There isn't a set one. "Antynaukowy" (lit. "anti-science") is the most common I've seen, perhaps because it's close to a well-established term "antyszczepionkowiec" ("anti-vaxxer") - but most often, it's just any of the expression that contains the core term of "anti science" or "denying science", such as "antynaukowe poglądy" ("anti-scientific beliefs"), "zaprzeczasz nauce" ("you're denying science"), etc.