Open the App Store and search for "macOS Ventura". Click Get , which will open System Settings/Software Update to begin the ~12GB download.
To download a macOS Ventura ISO file, you have a few options, but be aware that directly downloading an ISO file for macOS Ventura from Apple's official website isn't possible. Apple typically provides macOS updates and installers through the Mac App Store or its software update mechanism. However, here's how you can obtain or create a bootable installer for macOS Ventura: mac os ventura iso download