And besides the steps described by belegdol, you also must do a make install on your Mac after successfully compiling, which populates the necessary libraries and plugins into the app bundle.
makes the qmc2-sdlmame.app bundle more complete? Would it help if I added this step to the CI?
ETA: attempting to run make install in github gets me permission denied:
https://github.com/belegdol/qmc2-mame-fe/actions/runs/8433457590/job/23095002377