This steps and links provided in this gist are significantly outdated (having been created in 2020) and should not be followed. I will look into updating them when time permits.
Raspberry Pi OS is a Debian Linux derivative for the Raspberry Pi. "KVM" is a native open source virtual machine management service for Linux workstations and servers that leverages QEMU and libvirt. There are a variety of recipes for getting Raspberry Pi OS guest virtual machine up and running on KVM. Having tried many of these, this is the one I now use. Tested on Ubuntu 18.04 LTS Desktop, with all that implies (YMMV).
This is a "just for fun" project that I don't expect to make serious use of. With several actual Pi boards around the workshop, being able to reliably run on an emulator isn't really a major need.