Question: Super Duper: cannot find the bootable drive upon startup
I have been using Super Duper for many years. Recently, when I try to use a bootable close upon startup, my iMac does not find any bootable clones. They reside on a Thunderbolt drive connected directly to my IMac. I have recently upgraded to High Sierra. So I made a clean bootable clone, erase drive then copy. Stilll when I do a restart, Hold the "Option" key upon restart, no bootable drives are found. any suggestions?
iMac (Retina 4K, 21.5-inch, Late 2015), macOS High Sierra (10.13.1)