Downloading a macOS installer is so frustrating. I don’t even want to go into how much time I’ve wasted on getting it to work.
Long story short, I’ve tried to download macOS High Sierra from the App Store, Terminal, or by clicking the link on Apple’s page. None of them worked!
The link on Apple’s page says it cannot connect to the App Store.
The Terminal method (softwareupdate --fetch-full-installer --full-installer-version 10.15) returned the error “Install failed with error: Update not found.”
Searching for it in the App Store did find the installer, but it soon said the requested version of MacOS is not available.
How can I get the OS installer to create a bootable USB?
I understand your frustration cuz I had the same experience.
The reason why the update is not found or not available is because it’s not compatible with your Mac.
Take my MacBook Air (Retina, 13-inch, 2020) as an example. It came with macOS Catalina (10.15) and will not download earlier macOS versions like macOS High Sierra (10.13) from the App Store or Terminal.
Try not to download it from the App Store or Terminal.
Use a macOS downloader like iBoysoft DiskGeeker for Mac. You meant to create a bootable USB installer, right? Then this tool is the perfect option, as it allows you to create bootable USB installers for macOS High Sierra and other versions.
You were unable to download macOS High Sierra because your Mac doesn’t support it.
The options to get it:
Use a third-party tool that allows you to download the macOS installer and easily create a macOS bootable disk. (For example, iBoysoft DiskGeeker for Mac.)