In the Windows-specific part of fs_create_directory_with_parents, std::wstring_convert and std::codecvt_utf8 has been deprecated starting in C++17, the latter because of https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2871r3.pdf, and the former because all standard facets that the function could use will be removed in C++26.

I've come across https://github.com/nemtrif/utfcpp, a header-only library to handle UTF conversions. Worth considering?