This project aims to use CI to automatically build and package ROS2 Foxy for macOS. This is already done for Ubuntu (all packages on apt) and Windows, but there's just no good alternative for macOS.
The Vanderbilt Robotics team has detailed documentation on using this repository. Here's the gist of it, though:
base is required for basic ROS2 functionality. (For base, follow the instructions in the release notes to get supplemental tools installed.)/opt/ros/foxy/.source each workspace (source workspacedir/setup.bash). You can add this to your .bashrc or similar so every time you open a new terminal, it just works.ros2 or rviz2 and see the magic happen.