As I write this I’m hoping I’ve solved it but maybe this can help I was trying to install HS on a PCIe SSD. There may be other problems. I had thought I updated the firmware. I guess the evidence is that I HAVE installed HS on two drives already so successfully. But ok. Now I have a problem that the installer KEEPS trying to install MacOS. I can’t get it to stop, no matter how many times I restart, shutdown, use the option key to select another boot drive, hold D for diagnostics - it doesn’t do any of that. It just continues to try to install. I then found the original MacPro install disk to select a new startup disk. None of my OS drives showed up. I think the original disk was too old. Snow Leopard. So i chose look for network disks. Any clue as to what is happening here? How can I get back to my boot drive? Any of three boot drives would be great! How can I stop the installer? I didn’t solve it btw.