Downgrade from Mojave to older versiones.

NicolásVanegas wrote:

My iMac is a late 2012 version and run Mojave has been very hard, the cursor-ball of colors appears every minute. I have decided to do a downgrade to El Capitan. With shift + option + command + r, I restored or deleted my hard disc (excuse me for my English) and installed the OS x by default (Mountain Lion). But after 5 hours of downloading appears the prohibited symbol (a circle with a Slash in the middle). Hope you can help me, thank you very much.

How to reinstall macOS from macOS Recovery: https://support.apple.com/en-us/HT204904

How to use Time Machine to back up or restore your Mac: https://support.apple.com/en-us/HT201250

How to upgrade to OS X El Capitan - Apple Support

https://support.apple.com/en-us/HT206886

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