Boot from external drive

I have a May 2015 MacBook Pro Retina 2.5GHz 15.4" currently running macOS 12.4 “Monterey”.
Having for many years had external backup drives for a series of Macs and being able to boot from those drives, I bought an Envoy Pro Elektron 2TB SSD drive from Other World Computing. Upon trying to copy the internal drive to the new external drive using Carbon Copy Cloner, I learn that it is a difficult and dangerous (?) thing to do.
I would hate to think that if the internal SSD fails the MacBook Pro will become a door stop.
How do other people cope with Apple’s new and, to me, weird operating system requirements?
For now I’m doing all my work with a 2017 iMac 27" running macOS 10.14.6 Mojave. I only have the MacBook Pro upgraded to the latest OS to run TurboTax.Yes, I assume not updating the iMac to the latest OS is a security risk.

On my 2017 iMac 27", the original internal Fusion Drive was really slowing down the system, so rather than replace it I got an external OWC Envoy Pro FX 2T SSD, installed (at the time) Big Sur cleanly, then booted from the SSD and used Migration Assistant to complete the move from to the external drive. I’m now running the SSD as my boot drive running Monterey 12.5, and the Fusion drive has given up the ghost with SMART errors. Best thing I ever did, the money on the SSD was spent wisely.

So I recommend that you do a clean install of Monterey on the SSD and then use Migration Assistant to bring everything over to the SSD, and use it as your boot drive.

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The MacBook Pro probably is APFS formatted, CCC can not clone the system partition (container). Use the Monterey installer to install the system onto your SSD and use Migration Assistant to copy your data.

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And after you’ve used the Apple installer to install Monterey, CCC will have no problem smart updating your data partition per your set schedule. That’s what I’m doing. The key is you have to use the Apple Monterey installer to first install the system on each external partition you want to update with CCC. Then they’ll be bootable. (Well, as long as they’re not RAID…Monterey flatly refuses to boot from a RAID array.)

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