Follow the instruction on the installation page by the Manim Community to install Manim on MacOS. In short:
# Optionally, create a virtual env for manim
conda create -n manim python=3.8 -y && conda activate manim
# Install required dependencies for Manim
brew install py3cairo ffmpeg
# Required for Apple Silicon based machines
brew install cmake pango scipy
# Finally, install Manim
pip install manim
# Optionally, install dependencies for rending LaTex
brew install --cask mactex