User level: Level 1 (71 points)I connected the subject Macbook Pro M3 to my new MacBook Pro M5. Entered DFU mode and first tried to revive it and then tried restoring it. Both efforts failed with unknown error 21.
Posted on Oct 25, 2026 3:38 AM
User level: Level 1 (71 points)Oct 25, 2026 6:36 AM in response to Wink3
Problem solved. I wasn't entering into DFU mode properly for Apple silicon. Namely I wasn't holding all 4 keys in for 10 seconds, then continuing to hold the power button. Apple's instructions were not very clear on this.
User level: Level 7 (22,314 points)Oct 25, 2026 3:59 AM in response to Wink3
More details, please. macOS versions? Did you try another USB-C to USB-C cable that supports data and charging? Via Finder or via Apple Configurator? Did you try different port on the Host Mac? Via wi-FI or via Ethernet? Did you reboot the router?
How to revive or restore Mac firmware - Apple Support
User level: Level 1 (71 points)Oct 25, 2026 4:18 AM in response to Matti Haveri
The M3 is on Tahoe, the M5 on Golden Gate. The cable I used was from Apple. I used Finder as there was no need for the Configurator. I'll try a different port on the Host.
Originally posted at discussions.apple.com/thread/256382540