Did you reset the boot sequence of drives in the BIOS so it goes far enough to find the clone? Is it stopping on another non-OS drive before it reaches it?

There are a couple of external drives I've used with past desktops that I realized were somehow appearing as bootable in the BIOS but they didn't have the OS. The computer would hang instead of booting if they were powered up when I turned on the machine even though the C drive was listed first. They weren't supposed to be in the BIOS sequence but somehow they were, or it read them also as C?

SSDs are pretty inexpensive these days. External hard drives are pretty affordable also. The challenge becomes knowing which is which by labeling them for future use (or set aside as a backup).