Which versions of macOS can run in a VM? Can they run Intel apps too, and Intel macOS? How well do they perform? Can they access iCloud and run App Store apps?
Virtio
Two watersheds that could occur in macOS 15: that it only supports Macs with Apple chips including an Arm processor, and that it opens access to older versions of macOS on Apple silicon.
From Hypervisor APIs in OS X 10.10 Yosemite in 2014, through early VirtIO kernel extensions in Mojave in 2018, and Arm hypervisor support in Big Sur.
Before Apple had even released its Developer Transition Kit, virtualisation was already one of the 3 pillars of software support on Apple silicon Macs.
Once the virtualisation app has configured a VM to be run, it starts it, and stands back as the macOS Virtual Machine Service does all the hard work.
The Eclectic Light Company 