MacOS host - VirtualBox - MacOS guest

Download the Catalina full installer from the Mac App Store, and look for it in the /Applications folder. Once you retrieve and install VirtualBox 6.1.12 (or later when available) and its available corresponding extension pack, you will need to follow the included VirtualBox manual for configuring the guest to locate and use that macOS .dmg. I believe VB will use the Catalina .dmg directly without a need to convert it into .ISO format.

VirtualBox support for macOS is still experimental and there are no guest additions available for macOS guests. Thus graphics and performance will not be a pleasant experience. A 16GB MBP will be the minimum RAM solution. Be certain to exclude your Guest container in the Time Machine preferences, or you will be backing up 60 - 80 GB everytime you use it. Be prepared for your MBP to run hot while using Catalina as a guest in VB.

Once you have your guest set up, you may want to manually extend the available VRAM beyond 128MB to a maximum of 256 MB. You can do this in the Terminal:

VBoxManage modifyvm "Guest name" --vram=256

Apple does not distribute ISOs. The page you linked to is only updates, not full OS installers.

For Catalina, you would download the full .dmg installer from the App Store. How you would use it to install within VM I don't know as I've never tried it.

VikingOSX wrote:

VirtualBox support for macOS is still experimental and there are no guest additions available for macOS guests.

FWIW, there are in fact GAs for macOS guests although I can't speak to how well they work.

See: https://forums.virtualbox.org/viewtopic.php?f=22&t=90798&start=30

Be certain to exclude your Guest container in the Time Machine preferences, or you will be backing up 60 - 80 GB everytime you use it.

The only caveat would be if something goes wrong with a guest you would have to recreate it if you don't back it up in some manner.

Well yes, it would be good to have at least an initial backup of the guest, whether on Time Machine, or as an exported OVF2 appliance on another external drive. Not sure I would want to deal with backing it up every single time that I use the guest though.

Well honestly, I only installed a macOS guest some time ago, and ditched it due to horrid performance — but I did stay at a Holiday Inn Express, and have the impression that the DarwinGuestAdditions are not up to par yet.

Agreed. I also watched VirtualBox eventually destroy my Linux 18.04 LTS and 20.04 LTS guests over the course of a few months, where they were no longer bootable, and produced an error dialog not mentioned by anyone on the VB forums.

So, now I am running a small xyz-brand puck computer with a quad-core celeron behind the U55 model Sceptre ($230) TV that upscales the 1080p from the puck to 4K. Using the Cinnamon Desktop Environment and it is working perfectly. Thinking about VMware and the annual "dues" to keep it current for the macOS.next.

The official site for VirtualBox is here:

https://www.virtualbox.org

See: [HowTo] Create OSX ISO from the OSX Install app

It would be in the Applications folder. "Install macOS Catalina".

I for one gave up on macOS guests in VirtualBox long before the GAs became available. I don't have the energy or inclination to fuss with them now.

I have a 17" System 76 laptop I haven't booted for at least a year. I suppose I should update it sometime.