To obtain a working version of macOS High Sierra 10.13.6, you can use these methods: Official Apple Support

(via softwareupdate terminal command):

Open this Apple support link: https://support.apple.com/en-us/HT211683 (Scroll down – it lists High Sierra)

It was a typical Monday morning for John, a freelance graphic designer. He was sipping his coffee and getting ready to tackle a new project when he realized his MacBook was still running on an older operating system - Mac OS Sierra. He had been putting off updating it for a while, but with a new project requiring the latest software, it was time to make the switch.