Some suggest that if your SSD isn’t Thunderbolt, try connecting it via a USB-A port, although that doesn’t help those with MacBook Air or Pro models a Thunderbolt 3 SSD, such as a Samsung X5, freshly formatted in APFS (unencrypted) and connected to one of your M1 Mac’s Thunderbolt ports if you only have SATA SSDs which connect via USB-C rather than Thunderbolt, you may be successful, but it seems unlikely.an M1 Mac if you haven’t got one yet, I’m afraid it’s far too late for Christmas.
Thanks to many comments but no real clues, I’ve now been able to solve this, and here explain how you can do this too.
Last week I described how I had been unable to get either of my M1 Macs to start up from an external disk.
