Apple's official support documentation concerning the Device Firmware Update (DFU) port on newer MacBook Pro models with Apple silicon appears to be incorrect, according to reports circulating this week. The documentation specifies which USB-C port acts as the DFU port, a distinction that proved critical during an external macOS update attempt on a 16-inch M4 MacBook Pro.
Specifically, the support article instructs users that the DFU port on 14-inch MacBook Pros with M4 or M5 chips is the rightmost USB-C port when viewing the left side, while all others use the leftmost port. However, testing conducted by an independent developer suggested the opposite was true for their 16-inch M4 Pro machine, indicating a potential documentation oversight across configurations.
This port identification became mandatory when attempting to update macOS on an external boot volume, as Apple mandates that external storage devices must not be connected to the DFU port during the installation process. A user detailed repeated update failures when the external SSD was plugged into the port designated as the DFU port by the official guide.
The update process failed repeatedly, cycling through download and reboot stages before reverting to the original software version without providing an explicit error message about the port configuration. The user noted that command-line tools and System Settings offered no diagnostic feedback explaining the root cause of the installation failure.
Further investigation led to supplementary guidance suggesting security policy authorization issues with external drives, which required booting into Recovery Mode to resolve. While fixing the LocalPolicy allowed normal booting, the macOS update issue persisted until the external drive was physically moved to a different USB-C port.
Upon relocating the drive to the port identified as the non-DFU port based on the failed attempts, the macOS update to version 15.7.3 completed successfully on the first try. The developer cited frustration that the system initiates a lengthy update process only to fail silently rather than flagging the incorrect port usage immediately.
This incident highlights the fragility that can emerge when software update safeguards rely on specific physical hardware configurations that are not clearly communicated or error-checked by the operating system itself. The experience contrasted sharply with the expectation of seamless functionality often associated with the Apple ecosystem.
For users managing multiple boot environments or external testing volumes, this documentation error underscores the necessity of cross-referencing official guides with community findings for complex operations on Apple silicon hardware. The resolution required combining steps to fix security settings and physically remapping the connection port.
