You can run iOS 12 on QEMU: https://github.com/alephsecurity/xnu-qemu-arm64
Probably this fork[1] could be a good starting point.
The irony is that this is happening in QEMU; and was only about five posts above this one on HN:
https://news.ycombinator.com/item?id=28551264
https://github.com/alephsecurity/xnu-qemu-arm64
There is a project [1][2] to emulate iOS in QEMU. You can find more details about installation process and research itself in their articles [3][4].
[1] https://github.com/alephsecurity/xnu-qemu-arm64
[2] https://github.com/alephsecurity/xnu-qemu-arm64-tools