Is it possible to get macOS running in a Docker container?
Yes you can run macOS in a Docker Container: https://github.com/sickcodes/Docker-OSX
It has very low overheads because it's all real KVM nested virtualization.
I have stress tested it and the minimum requirements is about 2.5GB of RAM per container. The Docker container is Arch but it has very low overheads.
Make your own container:
# Catalina
docker run -it \
    --device /dev/kvm \
    -p 50922:10022 \
    -v /tmp/.X11-unix:/tmp/.X11-unix \
    -e &quot;DISPLAY=${DISPLAY:-:0.0}&quot; \
    sickcodes/docker-osx:latest

# Big Sur
docker run -it \
    --device /dev/kvm \
    -p 50922:10022 \
    -v /tmp/.X11-unix:/tmp/.X11-unix \
    -e &quot;DISPLAY=${DISPLAY:-:0.0}&quot; \
    sickcodes/docker-osx:big-sur

Or if you want to fast-track, or use CLI only, you can boot straight into a real headless MacOS command line using :auto
docker run -it \
    --device /dev/kvm \
    sickcodes/docker-osx:auto

You'll drop into the Darwin shell.
Extra options:
Visual display:
    -e &quot;DISPLAY=${DISPLAY:-:0.0}&quot; \
    -v /tmp/.X11-unix:/tmp/.X11-unix \

Add SSH:
    -p 50922:10022 \

Change resolution
    -e GENERATE_UNIQUE=true \
    -e WIDTH=800 \
    -e HEIGHT=600 \