If the App Store method fails or blocks you due to your current hardware age, you can use built-in terminal tools on any modern Mac to fetch installers directly from Apple's software update servers.
If you're looking for alternatives to downloading macOS High Sierra (10.11), consider: If the App Store method fails or blocks
Older legacy Macs (such as Mid-2007 to 2009 models) that do not meet the hardware requirements for newer macOS versions. If the App Store method fails or blocks