Catalina 10.15.4 Supplemental Update Has Issues

I am not sure how many people this long post will help, but hopefully it will help some:

I was unsure why my MacBook Pro would install this supplemental update without a hitch, but my one month old iMac would not. Every time I rebooted my iMac, even after a Time Machine restore that seemed to work, I would get the circle/slash symbol and not be able to boot up my machine. After texting Apple Support last night, they advised that I should bring my computer in as it seems like there is a hardware failure. I didn’t see how in the world that would be possible with just a software update and a brand new machine.

This morning, I called Apple Support and talked to someone who was really great. She was very helpful as I discussed the issue. And then we tried something different. I removed all external hard drives and my CD-ROM drive and then booted up my machine. I was shocked to see that it booted up just fine. No dreaded circle/slash symbol. When my machine was back up, I then installed the supplemental update, this time without any issues.

There is one issue that is still there and that is if there are any externals attached when rebooting my machine, it will give me the slash/circle symbol and not boot up properly, but when they are disconnected everything is fine. Obviously, this is annoying and something that needs to be fixed, but at least I know that it is not a hardware issue with my computer and I don’t need it serviced.

Catalina has been a nightmare of an OS. I am hoping that these issues are finally taken care of and that there is a stable system put into place soon.

Try booting into Safe Mode and download and apply the macOS Catalina 10.15.5 Combo Update.  The Combo updates are the safest to apply as they contain all of the updates since 10.15.0.

So after waiting a while I forced a power cycle. Got the normal password login screen, but about halfway through the boot process after sign in it kicked over to "Reinstall MacOS" mode. Went through the reinstall process and is now booting normally.

I can't tell if the supplemental update is installed but it's not showing any available updates. This was all on a 2012 iMac, my wife's 2020 MacBook Air handled the update without issue.

I have the exact same model iMac as you, and the supplemental update was also a problem for me. Had the black boot screen with white Apple logo up for an hour and a half (no progress bar) before I shut it down by holding in the power button and pulled the plug from the back. After a minute, plugged it back in and powered it up. This time got an Apple logo with a progress bar that eventually showed 30 minutes estimated, quickly followed by a 15 minute estimate, and right around that time the installation completed and I could log in. And every Catalina update gives me that Relocated Items folder, even though I delete the alias and the actual folder.

Catalina has been the first macOS that has been a problem for me, but a spotty problem. The first installation was a nightmare, but the other updates all went as expected, up until this supplemental update.

Solved the problem:

10.15.4 Supplemental Update was not working.  Mac Mini 2018 went through the motions but after restart, the upgrade was not done and the OS flagged to do the same update again.

Performed a T2 Firmware revive/restore with Configurator2, as described here:

https://support.apple.com/guide/apple-configurator-2/revive-or-restore-mac-firmware-apdebea5be51/mac

Configurator terminated with an error „cannot restore... timed out“, yet it apparently updated the firmware from 1037.100.359.0.0 (iBridge: 17.16.14263.0.0,0) to 1037.100.362.0.0 (iBridge: 17.16.14281.0.0,0). This appears to be the latest and is identical to what I have on my 2019 MBP 16 in.

After that, 10.15.4 Supplemental Update went fine. “Your Mac is up to date”

Quick update:

1. Was able to restore my bricked 2018 MBP 13 using Apple Configurator 2 using a lot of trial and error. Lots of failed attempts! This unfortunately meant wiping the unit though.
2. You can do this, provided you have another Mac that is running Catalina and follow the correct steps as people have been posting. Be aware - this wipes everything!
3. Apple actually reached out to me to discuss the issue in detail, so while their presence may not be felt on here, they're definitely taking this one serious.

Good luck everyone! Not a good experience.

The update was unremarkable on all my Macs. Try it again.

Back up your Mac as a matter of course: Back up your files with Time Machine on Mac. A Local Snapshot is created hourly and immediately prior to all macOS updates. If necessary restoring one takes all of two or three minutes.

Maybe you can turn off auto update? Auto download can be turned on but then you manually install it after backing up. Am hoping these are just random issues with  updates and not become a new normal.

I have pretty much an identical problem - with iMac (Retina 5K, 27-inch, Late 2014) - since upgrading to 10.15.4 Supplemental Update. In my case the system boots up and then after sometime (hour or so) crashes back to the Prohibited (No Entry) Sign Screen - like the following

https://support.apple.com/en-au/HT210901

From Recovery Mode I have run Disk Utility (Disk is Clean, SMART status is verified), Have re-installed MacOS (at first thought this had fixed it) but it always drops back to the same screen. Today ran Etrecheck and that indicates that I could have a failing disk - but given the number of people with same problem I suspect the update is the root cause...

This was the discussion I opened

https://discussions.apple.com/thread/251334078

ps. my MAC was bought in 2018. How long will be fixed those bug?

I have a 2018 Mac that doesn't display any of those problems.

The "bug" in your Mac will be fixed when you figure out what you have installed that is causing the problems.

For power issues, do an SMC reset.

I don't know what might cause Preview to crash. Try running it while booted into Safe Mode, and also in another user account (Guest is sufficient).

From your description it seems the update didn't go well, at least initially. That's always a possibility, and all the more reason for having a backup. If something is going to fail (even hardware) there is a greater likelihood of it happening during an update or upgrade, and always at the worst possible time.

I have multiple backups: this ain’t my first rodeo. But it’s the first time in a very long while that I can recall an update borking my Mac like that. Like Tim, I suspect there’s an issue with this one.