I’m trying to create a bootable USB thumb drive with OS X El Capitan 10.11 but unfortunately my iMac 20 (mid 2007) doesn’t see the USB device when start the boot manager while holding the “ALT” key. The current OS (Linux Mint 19.3 “Tricia” x64) is able to see the device, (I attempted to create the bootable USB using this iMac running Linux Mint). I was able to flash the USB thumb drive without any errors and it pass the validation with success. The .dmg file was downloaded directly from the Apple’s web site.
Some help will be appreciate,