Can't update macOS to Catalina 10.15.8

Should the 'Software Update' tab in System Profile

shows an update, carefully check & see what it is.

Sometimes that appears may be a later version than

your Mac could run; or in this instance, Big Sur OS11.

And your Mac maybe could run Big Sur; but that might

appear as 'an update' to Catalina, within Software Update.

• macOS Big Sur 11 hardware requirements
• macOS Catalina 10.15 hardware requirements

Good luck! ☺︎

If you try the update and it really is an upgrade to Big Sur, that may not work anyway.

Especially if your MacBook Pro is not listed as compatible for 'Big Sur' macOS11.x

But from what I've found after several intensive searches, including Apple's database:

I've seen no such animal: No macOS 10.15.8 in the wild; or walked in a park on a leash.

The download installer links "How to get old(er) versions macOS..." download article

gets you the last full download; even newer security updates could now be included.

And there's also a 'bootable installer' download article; that downloads a last Catalina.

That's not generally used, except for situations where no other installer works.

Nothing's wrong with your Mac; mine are older. With exceptions, once Safari browser

goes out-of-date, one could get other good browsers; such as Brave, or Firefox, & etc.

A good idea is to keep an older system and its Mac, as a backup configuration.

..At some point more volunteer contributors may appear, & state an opinion..

..CindyB3:

Do not confuse an upDate with and upGrade.

There is a listed 'last update' for Catalina 10.15.7:

(Download Security Update 2021-008 : Catalina)

https://support.apple.com/kb/DL2087?locale=en_US

Post Date: Dec 13, 2021

File Size: 1.49 GB

And it appears to include earlier ones; shows it installs over 10.15 to 10.15.7.

Be advised. These will be fewer and farther between as time goes by.

CindyB3 Said:

"Can't update macOS to Catalina 10.15.8P Can't update macOS Catalina to 10.15.8 from 10.15.7: I have 112Gb free space on the MacPro Mid 2012. Laptop appears to download and reboots. But then it still shows that 10.15.7 is live and there's an upgrade available. ??"

-------

Four Things...

A. Start with a Restart:

Having just now deleted all of this data, restart your Mac, trying this once more.

B. Boot Safe Mode.

When you boot in Safe Mode, login items do not open at log in, certain preferences are set aside, and damaged system files (i.e. caches) are fixed. To boot up in Safe Mode [Hold Down: the shift key upon boot]. So, on both Macs, boot into Safe Mode for 30 seconds, and then restart normally. For instructions, go here: How to Use Safe Mode on your Mac - Apple Support

C. Use a New Admin User:

Create a new administrator on this Mac (for temporary use), and see if you can perform this with this user. Once all is installed, login to the normal user, and delete these user you just created for the upgrade.

and...

D. Backup your Mac:

Important: Create a Time Machine backup of your Mac, so that you can have something to restore your Mac from, should anything go wrong with the update.

At this point, and evidence suggests there is no 10.15.18 update to Catalina pending;

the 'update' may be pointing to a next full system download-installer, Big Sur os11.x.

Nothing at Apple suggests this; and only security patches have been released in the

past year for Catalina, Mojave, & High Sierra. Support gets dropped on systems older

than previous three Years. Catalina would be next to no longer see security updates.

But maybe I'm incorrect.

Let's see what 6x6 says; or anyone else with some time on their hands & search engine.

As mentioned by K Shaffer, there is no macOS Catalina 10.15.8: The latest version is indeed 10.15.7. What you have installed is the Security Update 2021-008 for macOS Catalina 10.15.7. The security update does not change the version of macOS; this is why you are still seeing version 10.15.7.

If you want to make sure that you have installed the security update 2021-008, click > About this Mac and click the System Report button. In the System Report window, scroll down to Software and click Installations. Click the Install Date column header twice to sort in descending order. You should then see whether the security update is in the list.

The window should show something like the screenshot below. The only difference is that, for me, it shows the update to macOS Monterey 12.1. Yours should show the security update.

Open the Applications folder and move the macOS Catalina installer to the Trash. Empty the Trash (or just the installer) and restart your Mac. Then download the update again.