Installing Mojave on External Drive from Yosemite? How can I install MacOS Mojave on an external drive without updating my internal drive's currently installed OS: Yosemite?
There are a few tutorials floating around but they seem to be out of date, the ones I've found mention running the app store downloader, then opening the contents of the file Applications/Install macOS Mojave.app. I've downloaded the Mojave install files via the Install macOS Mojave.app but the downloaded files were placed on the target volume instead and don't match the file names that the tutorial lists.
The machine I'm using is a MBP113, on macOS 10.10.5.
It is compatible with macOS Mojave.
Make a USB installer by following this tutorial.  I would recommend the terminal method as that's the one I have tried and found reliable.  After you have made the installer, boot to it and plug in the external drive that you wan't Mojave installed on (which I'll refer to as the Mojave drive from now on).  Format the Mojave drive as APFS and GUID partition map with Disk Utility.  Finally, install macOS on the Mojave drive.