Unable to install High Sierra onto external SSD using MacBook Pro 2015 Catalina

Question

Unable to install High Sierra onto external SSD using MacBook Pro 2015 Catalina

Formatted external SSD using disc utility. Downloaded macOS High Sierra to MacBook Pro 2015 Catalina. After clicking on the download a box displays it is too old for the MacBook and does not proceed. Choice of installation disc is not given. Downloaded macOS Sierra and copied it to the external SSD. Tried to install OS but installation location was onto the MacBook and no choice of location was given. I want to setup an external drive to use some old software. Thanks

Posted on Jan 31, 2025 3:20 AM

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Answer 1

Top-ranking reply

dialabrain

Level 10

137,403 points

Jan 31, 2025 6:11 AM in response to donaldfrombrisbane

You have to create a High Sierra bootable installer. Boot your Mac with it, then choose the external drive to install it.

Create a bootable installer for macOS - Apple Support

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Answer 2

Feb 2, 2025 3:38 AM in response to dialabrain

Thank you for your reply. I could not create a bootable USB -file or directory not found. However I was fortunate to be able to access another computer which had macOS High Sierra and was able to download and install the OS onto the external SSD.

Again thanks

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