Cannot Reinstall MacOS High Sierra

I have an older model iMac that cannot be upgraded past High Sierra. I'm preparing to sell it and I wanted to clear out any personal information.

• • I booted from Recovery and used the disk utility to Erase the MacOS partition.
  • Back in the Utility window I selected Reinstall MacOS
  • The reinstall fails with the error "Could not create a preboot volume for APFS install"

I read somewhere that for the reinstall to work, the partition has to be in Mac OS Extended (Journaled) format. I used the Disk Utility again to reformat the partition MacOS to Mac OS Extended format.

Bad Choice: The Mac only boots into Recovery mode now and doesn't see the disk when I try to reinstall the OS again.

So, I downloaded the Install package for High Sierra and copied it to a Flash drive. I reboot the Mac with the Option/Alt key pressed and I get as far as selecting the Flash drive as a boot device. I then get the Apple logo and "processing" bars for a few minutes. Then I get a white screen that highlights the power switches on the mouse and keyboard.

My goal is to get this iMac back to the factory setup, Welcome to Mac screen

Any help is greatly appreciated.