support.apple.com/mac/startup Circle with a line through it Error Message FIX

Description

Learn what to do if your Mac starts up to a circle with a line through it (prohibitory symbol).

Just to let you know - if you don't want to change/replace the internal storage , you can always just use an external hard drive and install macOS on that external hard drive and run your Mac from there. This will start your Mac as if it new again and that's exactly what we ended up doing since its an older intel iMac