Made my own Windows 10 ISO with an autoanswer file but it won't boot

[DawnTreader]

You don't need to edit json manually. In the download there is a ventoyplugson.exe file (and .\ventoy\plugson.tar.xz)
Find the extracted files and run the .exe (or the linux .sh file).
https://ventoy.net/en/plugin_plugson.html
Just run the exe and you will get a browser based GUI where you can easily add XML entries.

If you want a step-by-step process, try my eBooks.

Yeah, I played with that today. It works awesome.