Mac won't boot up
my Mac won't boot up after installing the latest OS update
iMac 27″, macOS 10.15
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Hello, val47.
Can you get the Mac to boot in Safe mode? (hold the shift key down at startup). It can take much longer (10 min) to safe boot so be patient.
How to use safe mode on your Mac - Apple Support
Safe mode forces the OS to clear certain caches and logs and do other miscellaneous housekeeping. It's non-destructive to user data so is safe to do. Very often certain weird software behavior is corrected by simply logging in this way as a troubleshooting method. When you're in safe boot, the machine will not be at its best performance, especially with graphics, but that's normal.
Exit safe mode by restarting your Mac normally and re-evaluate the issue again.