Forget trying to setup your mac to use qmk, use docker instead.
First, install the Docker Application online: https://docs.docker.com/desktop/install/mac-install/
Run make git-submodule
Run docker build . -t mtseqmk:mtseqmk to build my custom docker image.
Manually launch the Docker Desktop App if not already running.
run ./compile_docker.sh
This should have created a file called handwired_dactyl_manuform_5x6_my_keymap.hex at the root.
Install QMK toolbox Flash by opening the hex file in QMK toolbox, resetting the keyboard bootloader, and clicking the Flash button.