Unable to install an older version of MacOS to MacBook

You will need to create & use a bootable macOS USB installer using the instructions in the following Apple article:

Create a bootable installer for macOS - Apple Support

When you mention "34 bit", do you mean the scanner is 34 bit, or the scanner software? If the software is 32 bit, then you would need to install macOS 10.14 Mojave instead as that is the last OS which supports 32bit software.

wbjimmy wrote:

I have a 2014 MacBook Pro running Big Sur and want to re-install an older OS ( say, Catalina?) in a separate volume I've created in my SSD drive. I don't want to replace Big Sur, I just want an alternative, OS to run a (34 bit) flat -bed scanner application that no longer works with Big Sur.

I appear to have downloaded the Catalina OS to my MacBook from the App Store but cannot install it. An error message says "This copy of the mac OS installer application is too old to be opened on this version of MacOS." Can someone please advise how I can proceed.

The Mid 2014 MacBook Pros originally shipped with Mac OS X 10.9.4 (Mavericks) and can be upgraded as far as the latest release of macOS 11 (Big Sur). So your MBP should be able to run Catalina.

If your goal is to run a 32-bit scanner application, Catalina is not the version of macOS that you want. It is the one that dropped support for 32-bit applications. I'd suggest installing High Sierra or Mojave on the alternative startup drive.

The question then is how to get Big Sur to let you run the installer application …

clicketyclack Said:

"Unable to install an older version of MacOS to MacBook"

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Verify Compatibility:

See my reply to your original post.

Glad you got things working. Thanks for the update.