For those that had an issue… I have a 2010 MBP that I tried this on.

On Step 14: “Choose the drive for the patches (the one where you just installed Mojave). Click patch after doing all of the necessary things above.”, my drive wasn’t displayed, my only option was the thumb drive. If I rebooted to my HD, I got a circle with a line through it, indicating no OS.

I was able to complete the install by re-booting to the thumb drive, opening Disc Utility, and “Mounting” the hard drive (click on your HD then click Mount).

Once the hard drive was mounted, my HD showed up in the MacOS Post Install, and the installation completed successfully.

Hope that helps!