The article might be correct and work on one device perfectly and without any problem.
Most of the website that creating content regarding the installation of Mac OS X El Capitan or macOS Sierra on VirtualBox is not complete and have errors. I may, eventually, see if qemu is faster, but that's even more arcane, so it's not likely in the short term.In this article, I’m going to show you the complete guide to fix VirtualBox errors while installing Mac OS X. In short, it does so much of what I need it to do that the commercial competitors don't have an appeal for me. I sometimes wonder if VMWare Fusion would be worth it, for the raw device support, etc., but I understand that it can be configured in VirtualBox, with patience and Terminal-fu.
For free (I, too, was tired of the "subscription model" annual upgrade pleas/threats), I really have to try to find a problem with it. Parallels seems to virtualize Mac OS more smoothly. It works well with most Linuxes I throw at it (have had some issues with Linux Mint and video drivers). I triple boot on my MacBook, but may toss that for using virtualized PCs.
Two-way clipboard support just works, and the granular control over the emulated hardware (how many cores, how much RAM, what size drive, etc.) makes it sweet for testing system parameters. It's not quite as nice to configure as Parallels, but once it's running it's fantastic. What can be said has mostly been said, but I'll chime in.
GUI: Fixed bug on Windows with inability to save taken screenshot under a folder with native name.GUI: Fixed crash on macOS Big Sur while browsing for an external image from First Run wizard.GUI: Fixed inability to complete First Run wizard after browsing for an external image.
Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers, it is also the only professional solution that is freely available as Open Source Software under the terms of the GNU General Public License (GPL). VirtualBox is a family of powerful x86 virtualization products for enterprise as well as home use.