Other links that may be helpful:

https://github.com/kholia/OSX-KVM

https://collaboradev.com/2018/10/19/arch-linux-running-osx-h...

Note that this violates the macOS licensing conditions unless you're running on Apple hardware.

Wouldn’t that be quite slow?

The key here is GPU passthrough, giving it real graphics hardware means that it's near native (there's still overhead, but it's on the order of 5% compared to completely native).

Works on my machine. There's virtually no difference between bare metal. Of course you need enough cores and dynamic memory (GPU memory too) to run your host OS and macOS. No benchmarks but it feels snappier than my 2017 MBP.

If it's fast enough to run triple A video games at an accecptable stable framerate, it should be fast enough to run an IDE.