How to install macOS Catalina

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Level 1

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How to install macOS Catalina

I have a 2019 iMac running Big Sur and have discovered that TurboCAD does not work with Big Sur. TurboCAD is not yet available in a version that runs on Big Sur, so I need to get back to Catalina. I want to install Catalina on an external drive just to use with TurboCAD and leave the rest of my system as it is. I have a formatted drive ready to go but can't find how to get the Catalina Installer. I have found and downloaded an installer but when I try to run it, I get the error message "this copy of the macOS Catalina installer application is too old to be opened on this version of macOS".

iMac, macOS 10.12

Posted on Feb 13, 2021 9:38 AM

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Answer 1

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dialabrain

Level 10

122,735 points

Feb 14, 2021 2:17 AM in response to pauljt

You need to create a Catalina USB Bootable Installer, boot your iMac from it, then use it to install Catalina to your external drive.

How to create a bootable installer for macOS - Apple Support

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Answer 2

pauljt Author

Level 1

9 points

Feb 14, 2021 1:19 AM in response to rkaufmann87

Thank you very much for your quick reply. My external drive is not big enough to take the full reinstall from time machine. Is there a way to just reinstall macOS from the time machine back up without reinstalling the rest of the system. The only thing I want on the external drive is Catalina and the TurboCAD application.

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