Thanks to another commenter I found https://github.com/evansm7/vftool/issues/2#issuecomment-735455161 https://github.com/evansm7/vftool/issues/2#issuecomment-73

Thanks to another commenter I found https://github.com/evansm7/vftool/issues/2#issuecomment-735455161 https://github.com/evansm7/vftool/issues/2#issuecomment-7354... which is exactly what I needed for Ubuntu 20.04: the idea to use cloud images which bypasses the silly installer.