Correct External SSD format, using as startup disk

Hi again Jack

SSD external drive not visible in SysPrefs



I made sure to format the external SSD as APFS, but it's still not visible in System preferences>Startup Disks. I've read that the standard approach is to restart and press CMD+R, then choose the SSD as a startup disk.

BUT, when I do this, the iMac just restarts as normal - there's no option to select the startup disk. I'm running Big Sur 11.6.1

Can you suggest what's happening and how to rectify the situation?

Many thanks

Tony

Hi Jack

No, not separately. I copied the Mac HD to the SSD. I assumed that Mac OS would go over.

So, do I need to add Mac Big Sur to the SSD, and how do I do that? Sorry to be dim but I’ve reached the limits of my expertise.

Thanks again

Tony

Hi there Jack

I bought the iMac in 2015 so I guess it’s a 2014 model. The SSD is a SanDisk Extreme V2 1TB.

Thanks for your help

Tony