If you do not have access to MacOS, refer to the FAQ in the Usage section to build with GitHub Actions instead. You'll need MacOS to build, as you require Xcode from the App Store. Simply having Xcode ...
Using a cloud image with cloud-init is significantly faster than ISO mount install. In my environment, I can have Ubuntu up and running in under 1 minute. vmWare govc is used to deploy an ova to ESXi.