How can I download and then install a newer OS onto an external HD and use it as an alternate boot drive? 10.10.5 Yosemite on my Mac Mini will no longer support Cricut Design Space and I'm being forced to find an alternative since they at Cricut no longer want to support a browser-based interface.
Mac mini, OS X 10.10
Here is an Apple article on how to create a bootable macOS USB installer which also includes links to the macOS 10.11 to 10.15 installers as well:
https://support.apple.com/en-us/HT201372
Make sure to check that your Mac meets the hardware requirements for the version of macOS you are installing. If your Mac supports macOS 10.13+, but you have trouble installing it, then try to first install macOS 10.11 instead.
Make sure to have a good backup of your internal drive before trying to upgrade macOS on your system. I know you are installing macOS to an external drive, but there is always a chance a system firmware update or the macOS installer could modify the internal drive as well.
Here is an Apple article on how to create a bootable macOS USB installer which also includes links to the macOS 10.11 to 10.15 installers as well:
https://support.apple.com/en-us/HT201372
Make sure to check that your Mac meets the hardware requirements for the version of macOS you are installing. If your Mac supports macOS 10.13+, but you have trouble installing it, then try to first install macOS 10.11 instead.
Make sure to have a good backup of your internal drive before trying to upgrade macOS on your system. I know you are installing macOS to an external drive, but there is always a chance a system firmware update or the macOS installer could modify the internal drive as well.
Boot OS from external drive
