VirajS wrote:
Almost every app crashes instantly when clicking the icon in the dock. All the system preferences panes won't open. When rebooting, the screen goes black and I can see the mouse icon. When I do a hard reboot, the system reboots ok, gets to the desktop, startup apps launch. As soon as I start using apps, the system freezes, I get a rainbow wheel, and after a few minutes, everything starts working again. Oddly, the calculator doesn't calculate correctly (?!) i.e 6 x 3 = 3. After a few minutes of regular use again the rainbow wheel appears again and the iMac freezes.
The only thing that's changed or updated is the Safari and Mac Mojave update in the last week of March 2020.
Do you do not say what exact Mac /model /year /size /retina /TouchBar is this
or
what exact macOS you are currently running?
What exact update is this you are referring?
Boot into Recovery (Command R) and from the dropdown menu: Utilities> Disk Utility> run the First Aid on your Macintosh HD (and the "Macintosh HD-Data" volume as well if Catalina) If errors are found and repaired, run again until no errors reported.
Recovery: https://support.apple.com/en-us/HT204904
To trouble shoot further you can:
Try a SafeBoot https://support.apple.com/en-us/HT201262
Takes noticeable longer to get to the login screen, does a 5-15 minute disk repair before it fully boots up, and certain system caches get cleared and rebuilt, including dynamic loader cache, etc. Login and test. Reboot and test will take a little longer as caches get rebuilt.
This test will tell you if third party interference; extensions etc are not loaded in safe boot mode.
Test issue in another user (or guest user) account https://support.apple.com/en-us/HT204443
This will tell you if it a universal issue or isolated to your user/admin account.
You can always reinstall macOS on top of your existing macOS, from Recovery: https://support.apple.com/en-us/HT204904
