@lheckemann has some awesome gists: lheckemann’s gists · GitHub
For example, an aarch64 VM that builds and runs from my x86 host, with working keyboard!: nix-build aarch64-vm.nix https://gist.github.com/lheckemann/63c52f2115346e6c9bbc6ecdfde9f43b#file-aarch64-vm-nix
It’s not using the raspi3b machine in qemu though.
Also, one that will probably be helpful for my BTRFS Pi (mis)adventures: https://gist.github.com/lheckemann/f265f155e9e7a7d05028eacfa6e96114