As a result of a lot of help from this Listserve I was able to install Mac OS 10.13.1 (Sierra) onto an external hard disc for a Mac Pro running Mac OS 10.13.6. The external drive with Sierra installed shows up in system preferences. Problem is, when I choose that external drive and restart I get a black screen with a folder and a ? in that folder. Restarting with the option key held down on presents the option of starting from 10.13.6.
Suggestions as to how I can boot this computer (either from system preferences or another mechanism) so I can start from Sierra.
Rationale for needing this: I have an expensive research microscope with a camera and the company that made this research camera stopped supporting Macintosh software. Last software OS that it worked with was Sierra.
So…any and all help would be appreciated.