Downgrade 2019 Mac Pro to Catalina

Question

Downgrade 2019 Mac Pro to Catalina

The 2019 Mac Pro will arrive tomorrow. I will need to run Catalina because of two software programs that aren’t compatible with Big Sur. I am having difficulty creating a bootable drive of Catalina from my MacBook Pro that has High Sierra. Right now I am downloading a file from the apple store called “download macOS Catalina 10.15.5 combo update”. This file is 4.8 gigs.

when I attempted to create a bootable usb drive on the 2013 MacBook Pro(following apple instructions) with high Sierra using the install file in the applications folder and the terminal, it said the installer file was not correct and wouldn’t let me continue in the terminal. It was a very small file inside the application folder called “install macOS Catalina” I think.

is the 4.8gig file I’m downloading going to be what I need to make a clean MacOS 10.15 install on the new Mac Pro ?

does anybody have experience downgrading a new Mac Pro that shipped with Big Sur?

Mac Pro

Posted on Jun 20, 2021 2:19 PM

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Answer 1

Best reply

D.I. Johnson

Level 7

22,343 points

Jun 20, 2021 8:24 PM in response to BabbylonSound

No, your MacBook Pro with High Sierra isn't too old to recognize the Catalina installer. But I'm not quite understanding why you're having such a time with the download. The correct installer is 4.9GB in size and will install 10.15.7.

Make sure you're using Safari when you try to download the installer. I do know that Firefox has been reported to have problems and I'm not sure about Chrome. Stick with what we know works.

You might have a look at this Apple Support document - How to reinstall macOS:

click > https://support.apple.com/en-us/HT204904

This paragraph in particular...

"On an Intel-based Mac: If you use Shift-Option-Command-R during startup, you're offered the macOS that came with your Mac, or the closest version still available. If you use Option-Command-R during startup, in most cases you're offered the latest macOS that is compatible with your Mac. Otherwise you're offered the macOS that came with your Mac, or the closest version still available."

I believe this would be macOS Catalina if the Mac Pro did in fact originally ship with that OS.

It might be worth waiting until you get the machine and see if you can take advantage of that option before subjecting yourself to more aggravation on the path you're currently walking.

Another option is that if the Mac Pro boots into Big Sur when you get it, you can use it to download the Catalina installer from the App Store using the link I included previously. Then create the bootable installer using the Mac Pro.

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Answer 2

Jun 22, 2021 12:37 PM in response to BabbylonSound

This is what I know so far.....

open the new 2019 Mac Pro and boot up into Big Sur. Create an admin password and connect to your Apple ID. Restart and press cmd-r and go to the startup security tab under “windows” at the top. Change the security settings to no security which is the third option. Under that change to allow boot from anywhere. You’ll need the admin password for this.

restart again with cmd-r and go to disk utility. Enter disk utility and erase the Macintosh HD system drive. I had to do this before it would ever allow Catalina to work.

then boot up again and press Option. Select the usb drive with Catalina. It will restart into the recovery screen but this time it will have Catalina as the second option instead of Big Sur.

I have described these steps to the best of my memory. The T2 chip setting with the admin password and reformatting the disk preinstalled with Big Sur seem to be the only thing different from past downgrades I’ve done for music software compatibility.

I think it might work by downloading Catalina from the internet in recovery mode, but my connection is slow so the USB drive I made seems to work

im also gonna try to turn the security settings of the T2 chip back to default afterwards.

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Answer 3

Jun 20, 2021 2:50 PM in response to BabbylonSound

The file you want to download and use for creating the bootable installer is not the combo update you mentioned in your original post. It's the application installer that you can download from the App Store at this link:

click > https://apps.apple.com/us/app/macos-catalina/id1466841314?mt=12

If it opens immediately after you download it, just quit it and then proceed to create your installer using Apple's instructions.

Create a bootable installer - Apple Support > https://support.apple.com/en-us/HT201372

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Answer 4

Jun 20, 2021 2:36 PM in response to D.I. Johnson

Will I be able to do a factory reset on the 2019 Mac Pro and get back to Catalina, if it has Big Sur. I’ve heard it might be difficult because of the T2 chip controller for the ssd. I hope I can make a usb boot drive with Catalina. But I can’t even seem to do that on y MacBook Pro.

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Answer 5

Jun 20, 2021 2:59 PM in response to D.I. Johnson

That’s what I’m having a problem doing. When I download the install Mac OS Catalina file from the apple store, I get a file by that name that is 19.2mb in my application folder.

when I open terminal and use the command to make the usb drive, terminal tells me the install file is not correct.

I will try it again and reply with the exact message.

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Answer 6

Jun 20, 2021 3:14 PM in response to BabbylonSound

But the photo didn’t work from my iPhone!

terminal says :

/Applications/install macOS Catalina.app does not appear to be a valid OS installer application.

this is the file I downloaded from the apple store called Catalina. When I push the button that says “get” it adds a file to my applications folder called “install macOS Catalina” But the file is only 19.1 MB.

im going to try and change my camera settings on my phone to a lower quality photo so that it might add the picture

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Answer 7

Jun 20, 2021 3:29 PM in response to BabbylonSound

Delete any other macOS installers that are in your Applications folder and empty the trash.

You may want to restart your Mac at this point also.

Download a fresh copy of the Catalina installer at the App Store link I provided above and try again to create your bootable installer using the Apple instructions.

The following from Apple Communities contributor @BDAqua regarding corrupted installers:

"If you get a corrupted message...

Naw, it's not damaged, it's just that you have an old copy already in Applications, there are 2 cures...

Disconnect from the Internet & set the Date back to 2014, then you can run the Install MacsOS ******* App in Applications, so expired Certificates are not expired.

Trash the Install MacsOS *******.app in Applications then a new copy more recent version can be downloaded."

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Answer 8

Jun 20, 2021 3:42 PM in response to D.I. Johnson

Thank you for your help. I’ve already deleted the installer from the applications folder and emptied the trash and attempted the Apple store download again. But I might have restarted first. I’ll try it again in order you suggested. I’ll get back with you in just a little while after I try it in this order like you suggest.

im wondering if High Sierra on my 2013 MacBook Pro is too old of an OS to recognize the installer for Catalina which is several versions later. If this method doesn’t work I will make a time machine backup of my high Sierra installation (since I must rely on this to function properly for work until later this week when the new Mac Pro is running)and then I’ll update to Mohave and try again.

thank you for your help

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Answer 9

Barney-15E

Level 10

112,668 points

Jun 20, 2021 7:22 PM in response to BabbylonSound

I get a file by that name that is 19.2mb in my application folder.

That is what is referred to as the "stub" installer. It just contacts Apple's servers to download the installer when it runs. You cannot make a bootable installer from it.

If you are running an OS previous to the one you are trying to download, then you will get the stub installer.

You can try to get the full installer through the command line, https://scriptingosx.com/2019/10/download-a-full-install-macos-app-with-softwareupdate-in-catalina/

I think Catalina is 10.15.7.

Or, you can wait until you have the new Mac and download the full Catalina installer from the previously posted link.

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Answer 10

Jun 20, 2021 8:37 PM in response to Barney-15E

Thanks. I’ll try that link. Although I’m upgrading the MacBook pro(2013)with high Sierra to Catalina right now. I figured it had to be something like that. Maybe I will have better luck making a bootable usb drive with Catalina after the update.

best case scenario, the new Mac pro(2019) arrives with Catalina. That’ll be great. If not I will try cmd-shift-option-r at boot up and try to restore factory settings. Or else maybe the usb drive will work.

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Answer 11

Jun 21, 2021 6:16 PM in response to D.I. Johnson

i was able to make a bootable usb drive with Catalina. However I couldn’t do it on high Sierra. Once I did a time machine backup on the 2013 mbpr and installed Catalina, then I was able to make the bootable drive.

im about to open the 2019 Mac Pro. I’ll update here when I figure out if I can downgrade the Mac Pro to Catalina.

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