How to install macOS Catalina on a 2013 iMac in VirtualBox?

I own a 21.5-inch, late 2013 iMac (with a couple hardware upgrades, namely RAM and hard drive) running macOS Catalina 10.15.7 (this is the latest macOS compatible with my specs). I'd like to run macOS Catalina 10.15.7 inside a virtual machine on my iMac. I'd like to use VirtualBox as the virtual machine because, unlike Parallels VirtualBox is cross-platform and free-of-charge, and unlike VMWare Fusion I am actually able to find VirtualBox online and download it. (Ever since VMWare has been subsumed by Broadcom, it has become very difficult to find a downloadable link to VMWare Fusion.) As a first step, I followed the link under the *Use the App Store* title on [this page](https://support.apple.com/en-ca/102662) in order to download the official Catalina installer. Then, thanks to [this answer](https://apple.stackexchange.com/a/278338/136773) , I ran the script in [this project](https://github.com/rtrouton/create_macos_vm_install_dmg) in order to convert Catalina's installation file into a bootable ISO file. I then followed the instructions under the *How to install macOS in VirtualBox* heading from [this page](https://www.xda-developers.com/how-install-macos-virtualbox/) to set up a virtual machine in my VirtualBox instance (v. 7.0.20). I used the following configurations: 1) 8192 MB memory size, 2) 64 GB drive size, 3) 2 processors. I followed all the steps up to and including step 15. I didn't know what do in step 16, and I also was a little apprehensive to follow it, because I didn't understand what it did. So instead of following step 16, I closed the VirtualBox instance, and then reopened it, and hit the Start button to start the Catalina virtual machine. The following screen of text messages appeared, and that's it. Nothing more happened. How can I proceed from here? How can I install macOS Cataline in VirtualBox? Would it be easier to install it in VMWare Fusion? If so, where can VMWare Fusion be downloaded from? There is a post similar to this one [here](https://apple.stackexchange.com/q/382303/136773) , but it's 4.5 years old, and I'm unable to figure out from the answers what I'm supposed to do.