This tutorial for installing macOS 13 Ventura has been adapted for Proxmox from Kholia’s OSX-KVM project and Leoyzen’s OpenCore configuration for KVM. You can get the full sourcecode of my OpenCore release on my GitHub here.
Since Ventura is still in closed Developer Beta, you need to be an Apple Developer and have access to a Mac (or Mac VM) to download it.
I’ll assume you already have Proxmox 7.2 installed. You also need a real Mac available in order to build the installer and fetch the OSK key.
Your Proxmox host computer’s CPU must support AVX2 (a new restriction in Ventura), so for Intel your CPU must be at least as new as Haswell. Older CPUs will panic and reboot while trying to boot the installer.
Modern AMD CPUs also support AVX2 and should work with this guide.
Since Ventura is still in Beta and support for it is preliminary in OpenCore, don’t expect full functionality (Beta software makes for a poor daily-driver).