Hypervisor.framework (and Virtualization.framework) in macOS run a Apple written hypervisor. This hypervisor implements VirtIO for its devices and can run macOS VMs (with full graphics and hardware acceleration, at least on the M1). One could conclude that it was implemented this way to allow compatibility for macOS on different hypervisors (and also so that Linux would just work on theirs).

Speculation: I would be surprised if there isn’t a team internally working on a stripped down variant of macOS (or just Darwin + drivers?) designed for deployment as a server so that they can drop a bunch of racks of Mac Minis (or, with budget, some kind of blade arrangement with a Apple Silicon chip on it) into a datacenter and build a huge build farm (using VMs to run iOS and macOS, or jails if they ever get some kind of container setup). It would be dramatically better than having to manage x86 and all that extra bloat of average servers once you got through the growing pains. And they could guarantee security way better.