macOS Mojave progress lost after restart

Hello, I have tried to download the new OS and it starts from nothing again once my "computer" restarts during the installation. I am using VirtualBox and I just need an OS that can download Xcode 10 so I can learn to develop apps.
My version is not compatible with the required one (10.12.6 and I need 10.13.6+) and the only other things that I can find are updates that also require 10.13. I luckily found Mojave today and I saw that I finally had an OS that could download Xcode 10 but I keep losing progress every single time because of the restart. What can I do to be able to download Xcode 10 or Mojave?

Welcome to our forums.

As of today, VirtualBox is not entirely compatible with Mojave. You can do some googling to read what work arounds are required before you can use it. What operating system are you currently using as it sounds like you're not able to update to Mojave?

Oh, thank you for welcoming me. I noticed that I was not clear when I said "it", which refers to Xcode. I am using 10.12.6 and I need at least 10.13.6 to download Xcode. I can download Mojave but it will not install due to progress being lost after it asks me to restart. Also, thank you for letting me know that VirtualBox is not entirely compatible with Mojave yet. I will search for a way to download High Sierra tomorrow but at the same time I will leave this thread open to suggestions if that is fine.

I am using 10.12.6 and I need at least 10.13.6 to download Xcode.

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Sadly, I think your problem will be getting macOS High Sierra. Almost as soon as macOS Mojave was available, High Sierra was withdrawn from the App Store.

On the other hand, given a little time, what you are seeking may become Mojave compatible.

Best of luck.

Ian