Since the MacOS system updates (minor version upgrade) do not work in Virtual Box (maybe somebody got it going, it does not work for me) I have decided to get my own Mac Mini and produce a usable MacOS ISO for installation in Virtual Box whenever a new version comes out.
I have followed this blog post to create the ISO for High Sierra 10.13.6 https://tylermade.net/2017/10/05/how-to-create-a-bootable-iso-image-of-macos-10-13-high-sierra-installer/
So there are no hacks involved in the ISO, all is valid stuff from Apple.
So on the freshly updated MacOS I have executed the following
hdiutil create -o /tmp/HighSierra.cdr -size 5200m -layout SPUD -fs HFS+J hdiutil attach /tmp/HighSierra.cdr.dmg -noverify -mountpoint /Volumes/install_build sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/install_build mv /tmp/HighSierra.cdr.dmg ~/Desktop/InstallSystem.dmg hdiutil detach /Volumes/Install\ macOS\ High\ Sierra hdiutil convert ~/Desktop/InstallSystem.dmg -format UDTO -o ~/Desktop/HighSierra.iso
And uploaded HighSierra.iso to my Linux system (Intel x86_64) Please be aware that the this won’t work for AMD CPUs since Apple does not support them.
You can get the latest 10.13.6 ISO here -> https://drop.me/ByWxnP
Next I have installed the High Sierra 10.13.6 exactly the same way as the previous version 10.13.5 https://astr0baby.wordpress.com/2018/06/11/installing-high-sierra-10-13-5-in-virtualbox-5-2-12-on-linux-x86_64/
Update from MrQuickFX to get Audio going in VIrtualBox macOS guest