The version "macOS 10.13.99" does not officially exist; the final release for macOS High Sierra was 10.13.6. Users encountering "10.13.99" are often seeing a confusing error message from an installer that requires a specific version of High Sierra already be installed before applying a smaller update.
If you are seeing an error that iTunes "requires macOS version 10.13.99 or earlier," it means you are likely on a Mac running macOS Catalina (10.15) itunes macos 10.13.99 download
If you meant macOS 10.13.6 (High Sierra) and need iTunes: The version "macOS 10
Notable features
Upgrade your Mac or macOS if:
Because "macOS 10.13.99" is a specific and unusual version number, this guide addresses the technical context of that version, why you likely cannot find a direct "10.13.99" download, and how to get the correct version of iTunes for your Mac. Click “Continue
iTunes.pkg installer.