VirtualBox only supports ISO and virtual machine image file so the first thing you need is to convert macOS DMG file to ISO. Part 1: Download macOS ISO File or Virtual Disk So in here, we will introduce a free way to create bootable macOS USB on PC by creating a macOS virtual machine with the help of free VirtualBox software. However, you won't be that lucky if you were on a Windows 10 PC. It is a lot of easier when it comes to creating macOS bootable USB installer on a Mac as it has built-in as well as third-party tools to do that.