https://forums.unrealengine.com/t/silent-build-blocked-by-unrealversionselector-on-windows/271955/2
This forum above has relevant information. The key is to edit the setup.bat such that you pass “/unattended” to then end of " .\Engine\Binaries\Win64\UnrealVersionSelector-Win64-Shipping.exe /register" (Order does matter). You will also want to run setup.bat with --force of course.