1
Diagnostic step 1
Do not attempt a filesystem repair that writes to the volume until you have a block-level copy; create a byte-for-byte backup using dd or a cloning tool to another drive on Linux where the device mounts read-write.
FULL AI ANALYSIS
External USB-C NVMe enclosure mounts read-only as APFS on macOS 12.6 after system update
Generated Oct 3, 2026, 12:35:03 AM
Analysis summary
The enclosure firmware (USB-SATA/NVMe bridge) is returning a read-only condition to macOS, likely because macOS 12.6 interprets a returned SCSI/USB status as requiring a read-only mount. The fact that the same NVMe is writable in a different enclosure and that diskutil reports I/O-level flags suggests hardware/firmware incompatibility rather than APFS corruption. Other possible contributors include tightened APFS mount semantics in macOS 12.6, changes in USB power management, or a transient file-system flag set by previous unclean disconnection.
Possible causes
USB-to-NVMe bridge firmware incompatibility with macOS 12.6 causing the device to advertise read-only
85%macOS 12.6 changed handling of certain USB error codes and forces read-only mounts on non-compliant bridges
80%Power delivery or hub-related issues causing the enclosure to fail write initialization
10%APFS metadata flagged as requiring repair after unclean removal and macOS prevents write access until verified
5%Suggested fixes
2
Diagnostic step 2
Test the NVMe in a known-good enclosure that previously worked with macOS to confirm enclosure vs. drive behavior (reversible swap test).
3
Diagnostic step 3
Check for firmware updates for the USB-C enclosure and, if available, apply them following vendor instructions; if vendor firmware is unsigned, avoid risky firmware flashes.
4
Diagnostic step 4
If you must work on macOS, mount read-only and copy data off the device; avoid disabling SIP or other protections without understanding risks.
5
Diagnostic step 5
If all evidence points to bridge compatibility with macOS 12.6, consider using the other enclosure or copying data to a new drive, and escalate to enclosure vendor support if firmware updates are available or if this affects multiple macOS machines.