“solved” for me :
Had the same using a late 2014 27” iMac. Lagging for each and every action. Spinning wheels. Slow boot.
i ended up reinstalling from scratch (no time machine restore) and now it works perfectly. I suspect it has something to do with the Fusion Drive : could
it be that the OS files ended up on the mechanical drive ?
pain in the *** anyway. First time since 2008 that I had to reinstall from scratch.
Pagaille
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