Manual software update download for macOSX 10.13.6 High Sierra

Go here: How to download and install macOS - Apple Support

Alternately, you can use commands in the Terminal to download specific versions of macOS:

• To download a major release version of the macOS installer:
  • softwareupdate --fetch-full-installer <major release number>
  • For example: softwareupdate --fetch-full-installer 13.0
• To download a specific version of the macOS installer:
  • softwareupdate --fetch-full-installer --full-installer-version <specific installer version>
  • Ex: softwareupdate --fetch-full-installer --full-installer-version 10.13.6

The softwareupdate program downloads the installer you requested to your /Applications folder (but doesn't launch it). Note: The last time I used these commands was in Feb 2024. I haven't had a need to try them recently, so I can't verify that they will still work.

10.13.2

Download macOS High Sierra 10.13.2 - Apple Support

10.13.3

Download

10.13.4

Download

10.13.5

Download macOS High Sierra 10.13.5 Update - Apple Support

10.13.6

106395

I've never done it but here's the links to the OS + individual updates

What updates?

10.13.6 is obsolete. There are no updates for it.