I believe it is this: in Big Sur system dynamic link libraries are not available as separate entities. They're pre-loaded. The -l switch for Apple clang still finds them without a -L switch. Gcc does not. There's no solution for Apple libraries. For C++ standard libraries, you have to install the libraries, they should come with g++ compiler if you're installing using brew. I guess the reasons: Faster loading, faster access, less VM manager resource use, and last but not least, vastly improved security (it stops hijacking).