On macOS, this repo currently ships gfortran and its libraries based on a modified version 11.3.0 https://github.com/isuruf/gcc/releases/tag/gcc-11.3.0-2
GCC 11 has reached EOL 6 months ago, so it seems like a good plan to upgrade to a newer version. I would be willing to help, if someone can clarify what the expectations are (I am a Homebrew and GCC maintainer).