Ok, so this is just OSX-KVM with extra steps. Seems like a very weird use case for Docker, but okay.
I recently wanted to build Python wheels for a whole bunch of Python versions and packages on Mac ARM64. I ended up using OSX-KVM, and then using cibuildwheel to crossbuild to arm64. Pretty dang easy.
I set up OSX-KVM (https://github.com/kholia/OSX-KVM) and it worked really well. Having archlinux is a huge plus for this (it's why the docker image uses it), as qemu is super simple to setup and get running. Was surprised how easy it was, but given how much effort the bootloaders have had over the recent years for Hackintosh, qemu users can just yoink that bootloader and use it.