My wife was ignoring nagging messages to update macOS Sierra on her 2011 MacBook Air so I did it for her, all good.
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- MacOS High Sierra (version 10.13) is the fourteenth major release of macOS, Apple Inc.' S desktop operating system for Macintosh computers. MacOS High Sierra was announced at the WWDC 2017 on June 5, 2017 and was released on September 25, 2017.
- MacBook Air (Mid 2012 or newer) MacBook Pro (Mid 2012 or newer) Mac mini (Late 2012 or newer). Question: Q: From MacOS High Sierra to Mojave Update?
I then installed the recommended update to High Sierra, when disaster struck. It was unusable, dreadfully slow, CPU activity at 300-500%, worked okay in Safe Mode.
After days of trying to work out how to revert to an earlier version, I installed El Capitan in a roundabout way. No installer would ever complete, so I installed El Capitan on a USB stick (installed it, not made an installer), then cloned that onto another. I then booted the MacBook into the first USB stick, then cloned the second stick onto the internal SSD after first erasing its contents with Disk Utility.
So—I thought—I basically had a fresh install of El Capitan starting from a clean slate.
For good measure I performed PRAM and SMC resets, so this is as close to a factory reset as you can get.
Yet... on rebooting, the MacBook is just as slow as it was after updating to High Sierra.
Activity Monitor reports %CPU at 400-500% with no apps open (except activity monitor) though no individual process is using very much at all.
In Safe Mode the figures look entirely normal and the laptop is responsive, except for so much screen flickering that it's not a viable alternative.
Mac Os High Sierra Mac Mini Mid 2010
I'm at a complete loss now as to what to do next.
Install Macos High Sierra
Are there any next steps?
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