I have been using macOS High Sierra, which is no longer supported by Apple. Today I erased my drive in preparation for giving the iMac to a friend, and I cannot reinstall High Sierra. How do I go about (re)installing an OS so the computer is usable?
iMac 27″, macOS 10.13
That iMac is limited to macOS 10.13 High Sierra, and that’s what you’ll want to install.
Here is how to get macOS 10.13: How to download and install macOS - Apple Support
If Option-Command-R works here, use that: Use macOS Recovery on an Intel-based Mac - Apple Support
Many thanks. New learning here is that Option-Shift-Command-R is possible solution (it's Intel-based but Option-Command-R did not work).
What OS to use when reinstalling on a 2011 iMac
