What was in the September 24, 2020 update that killed my iMac?

I had the same issue, my iMac Mini was not working anymore (Late 2012 edition). I will not upgrade to Catalina, because then some of the apps I need won't work anymore because no updates are provided in the latest Mac OS.

Fortunately I could recover everything via the recovery mode without deleting my personal data. But now I have a build from September 2019 - 2019-05 (18G103).

How can I upgrade again to Mojave build 2020-04 (18G6020)?

Same here, as reported in a similar thread. But by some miracle, I managed to reinstall the Mojave OS from a Time Machine backup, and now more or less everything seems like normal. However, I flatly refused to "obey" when the most recent request to install this Security Update appeared in an information box, and I won't install it before Apple has confirmed that the update is now bug-free.

I have never before had such a horrifying experience with Apple (been a user since 1988). Please Apple, stop inventing hundreds of new gimmicks all the time and concentrate on the important things. Most people out here NEED their computers permanently!

I think if we all start a new thread with, say, "Apple Software Update Sept 24 2020 Has Crippled My System", then Apple will maybe respond. So far, discussions are only going under one or two posts. They probably only notice headlines for individual posts, so they probably need to see lots of them.

We are used to it. Apple does respond to warnings from volunteers about "inmates" getting out of line and to answer posts that have not gotten answered by us volunteers.

I found your comments "OK".

R

Just to reply on my earlier report of the same problem people are experiencing here.

I was able to find a solution. The accountsd is taking too much CPU usage. My fans quiet down when going to my calender preferences and setting my updates to manual instead of automatically. Maybe inconvenient, but better than a sluggish macbook. I hope I can help somebody with this tip!

And a further update...what also helped was to go to the spotlight settings and request not to search on your Macintosh HD. That definitely did the trick for me. See also this link: https://apple.stackexchange.com/questions/182059/why-is-the-accountsd-process-eating-so-much-cpu

Mine did the same! Late 2013 iMac (21.5-inch, Late 2013), running Mojave 10.14.6 and ran Security Update 2020-005 on 09/25/20 AM. Wouldn't exit and had to power down then super slow to boot and work with anything! I Restored to Time Machine Backup completed just before the security update and all is better again. What is Apple doing? Releasing something like this is totally irresponsible! FIX IT APPLE!!!!!!

Multiple people are suffering effects from these two patch’s. A user named “Steve27” in another thread related to this issue mentioned this article:

https://mrmacintosh.com/mojave-2020-005-security-update-causing-major-problems-updated/

it was very helpful in explaining the scope of the issue but more importantly what to do about it.

basically

reinstall your MacOS, he explains how in the article.

then you will be faced with when to reinstall the two new updates. The order of the installation of those two updates is critical. Only one way works.

I reinstalled my OS, which was 10.14.6 and it fixed all of my problems, but I haven’t yet reinstalled the security update or the Safari update.

(User) Steve27 said he did the security update first and all was well. Then he lastly upgraded Safari and all was well. (Brave was he). You can search for his comments yourself to verify what he said and did. I can’t remember the name of the thread as I type this.

2 Keys for Restore...

1. Start up from macOS Recovery

To start up from macOS Recovery, turn on your Mac and immediately press and hold ...

Command (⌘)-R

Installs the latest macOS that was installed on your Mac.

I have the last of the old Mac Pro towers from late 2012 or 2013 I believe and it's non-functional now that I've installed this last security update, the display is not working, smc, pram, recovery mode have all been attempted, not sure if any of them worked, pretty frustrating as this is my main workstation, now trying to figure out how to boot into target disk mode to my new MBP with USB_C, i am sure that will be straightforward to connect via firewire 800...

I'm hoping some wizard can help. I have the same problem on my iMac.

Same here. After a few hours things seemingly returned on my late 2013 iMac.