can't boot from an external drive

[azrael2001ca]

Hi everyone.

First the "basics"
iMac running Catalina (10.15.7 - Late 2013)
Tried with two different size drives 2TB / 4TB.

I created a backup with Carbon Copy Cloner of my drive, and when it finishes, it says "Drive is bootable."

I shut down the system, waited for it to completely shut down, restarted with the power button and upon the chime I pressed option, but I never get the choose your drive option. After a given period it boots off of the internal drive.

I have selected the drive right in system preferences -> Startup disk, and I get the same thing.

During research, I read that you have to allow external drive booting on Catalina, so I shut down, restarted pressing Mac+R, got to the recovery and then selected Utility -> Startup Security Utility. I don't get the Authentication password request, I get a firmware request.

Anyone know how I can fix this?

Regards

 

[Racineur]

Hello. So many problems I don't have. My iMac 2013 (so old) boots with Catalina (or Mojave, or El Capitan, or High Sierra and even Sierra) from external SSDs. Original Mountain Lion resides on the internal 1.2 T Fusion Drive still. For the external SSD, I format de drive and I simply install any OS X or macOS version on that drive using the installer and chosing the drive before "Install". Never never had any problem other than Mountain Lion still boots faster and flies like a Saturn rocket compared to Catalina. And I have all of this lovely apps from 2013. My iMac is too old for anything over Catalina though. I know about Carbon Copy Cloner but wanted to try booting without its magic...