Imac will not restart
Older iMac (2016?) was powered down and will not restart.
I tried the usual fix, safe mode, but it stalls and recovery into Disk 1st aid, but that failed
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Can you run Apple diagnostics? https://support.apple.com/en-us/HT202731
If that doesn't run or show problems my next suggestion would be to reinstall MacOS. Preferably from a Time Machine backup I recommend everyone have, or alternatively from Internet Recovery.