In order to get this working, you will need access to a real Mac in order to download Sierra. You could, we suppose, obtain a Sierra ISO by other means, but we don’t recommend it. Borrow a friend’s Mac for an hour if you don’t have one, and you should be fine—everything beyond step one of this tutorial can be done on your Windows PC.

https://www.howtogeek.com/289594/how-to-install-macos-sierra-in-virtualbox-on-windows-10

Run macOS on your PC as a virtual machine : https://scottiestech.info/2016/09/25/run-macos-on-your-pc-as-a-virtual-machine/