You are correct. I am using an iMac (21.5 inch, Late 2013) with Catalina 10.15.7 and the same version of Virtual Box. I solved your problem by have the firmware boot from z file. I chose to boot from
The simple solution is to enter the following at the
I used a Snow Leopard ISO file created from a Snow Leopard OS X 10.6 DVD purchased from Apple. For more information, see this answer.
I needed to set the "Audio Controller" to
ICH AC97, otherwise Snow Leopard would not boot after the installation completed. This change results in a Snow Leopard without sound.
After installing, I immediately upgraded to OS X 10.6.8 by downloading Mac OS X 10.6.8 Update Combo v1.1 to the host, transferring to the virtual machine and installing.
I enabled the 64 bit kernel by entering the following command, then restarting.
sudo systemsetup -setkernelbootarchitecture x86_64
Guest Additions failed to install with the following popup message.
I had no problems installing Snow Leopard on a iMac (21.5-inch, Mid 2011) with High Sierra 10.13.6 and Virtual Box version 6.1.12 r139181 (Qt5.6.3). In other words, I did not need to change the "Audio Controller". I was able to upgrade to OS X 10.6.8 and enable the 64 bit kernel. However, Guest Additions failed to install with the following popup message.
I assume Guest Additions would have installed, if an older version of VirtualBox was being used.