Yes I use it all the time. I currently use it on a Mac Pro Tower from 2012 w/ 10.13.6. I can only upgrade to 10.14 with this hardware. Im thinking of getting a newer laptop but still want to be able to launch this older OS to use my Music production and Video editing software.Have you used the external to boot another Mac? Do you still have that Mac (and will continue to boot from the external on that older Mac?)
If no other Mac, then you could try upgrading the system on the external to one supported by the New Mac laptop.