Qt Creator does not recognize the std::string_view, std::filesystem::path, etc., because their definitions in the header files are "behind" the macro check:

#if __cplusplus >= 201703L

In the C++ Code Model Inspector in the Toolchain Defines:

#define __cplusplus 201402L

although for a C++17 it must be a 201703L.

A temporary workaround for the Qbs projects, when the cpp.cxxLanguageVersion: "c++17" is defined, is:

cpp.defines: ["__cplusplus=201703L"]