Create a MacOS Monterey install ISO

MacOS_Monterey_ISO.sh

# Download the installer for MacOS Monterey
softwareupdate --fetch-full-installer --full-installer-version 12.3.1

# Create a directory for the VM installer
cd ~/
mkdir VMs
cd VMs
mkdir installers
cd installers

# Steps below from https://www.youtube.com/watch?v=anB5DQ7brf0

# Create a DMG
hdiutil create -o ~/VMs/installers/MacOS_Monty -size 14500mb -volname MacOS_Monty -layout SPUD -fs HFS+J

# Mount the DMG as a Volume
hdiutil attach MacOS_Monty.dmg -noverify -mountpoint /Volumes/MacOS_Monty

# Use createinstallmedia to turn the Volume into an installer
# You'll need to enter your password for the sudo:
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/MacOS_Monty --nointeraction

# Eject the volume via the UI. You can see it in Finder on the left.
read -p "Please manually eject the MacOS_Monty volume. Hit Ctrl+C to abort this script. Otherwise press any key to continue. " -n 1 -r

# Convert the DMG to a CDR, Apple's format for CD images.
hdiutil convert MacOS_Monty.dmg -format UDTO -o MacOS_Monty.cdr

# Rename the CDR to ISO as expected by VirtualBox.
mv MacOS_Monty.cdr MacOS_Monty.iso