First, a quick clarification. Apple’s versioning for High Sierra ended at . If you are seeing references to 10.13.99, it is likely a placeholder reference or a typo for the "end of the line" for macOS 10.13.
The version is a placeholder used by the final standalone iTunes installers (like version 12.8.3) to signify that they are only compatible with macOS High Sierra (10.13) or older. If your Mac is running Monterey, Ventura, Sonoma, or newer, these installers will fail because the operating system already has the newer, integrated versions of these tools. How to Proceed Based on Your Needs itunes macos 10.13.99 download
Security & stability notes
To resolve this, you should download the rather than incremental updates. Recommended Downloads for High Sierra First, a quick clarification
If you are already on macOS High Sierra (10.13.0 or higher): The version is a placeholder used by the