Chosen Solution
I think you’re fighting a firmware issue. Don’t forget the newer OS’s use APFS and from High Sierra onward the OS installer updates the firmware to allow APFS boot up. So your system might be already updated and the drive (or boot up image) is unable to handle it as its older than High Sierra. I’ve also seen master boot records message up by malware! Often happens with dual boot or BootCamp based macs running <cough!> Windows! You may want to take the drive our and using a Windows or Linux system reformat it to FAT or exFAT so Mac Disk Utility is able to handle the drive when you put it back.
