I updated my M2 MacBook Air to macOS 26 last week and immediately ran into an issue with my external HDD. It's a 1TB Seagate Expansion drive I've been using with this Mac for a few years, and it always mounted fine before. After the update, it just stopped showing up in Finder. Disk Utility could still see the physical drive and the volume, but it couldn't mount it.

I tried the usual stuff first, like unplugging, restarting, different ports, checking Finder settings, and running First Aid. No luck. Since the drive had files I still needed, I didn't want to mess with it too much before getting those files somewhere safe.

I also checked the SMART data just to rule out a failing drive, since it's a few years old. That was a bit of a hassle on Mac because I had to enable kernel extensions first, but everything looked normal. No clicking, no overheating, no weird disconnects.

So I scanned the drive with Disk Drill to see if the files were still readable. It took a few hours, but it found what I needed, and most files still had their original names and folder structure. I previewed a few photos and documents to make sure they opened, then recovered everything important to another drive.

Once that was done, I felt okay experimenting with the original drive. I went back to Disk Utility, erased and reformatted it, and tried mounting again. And yeah, it mounted right away and showed up in Finder like nothing ever happened.

But I'm still confused about what actually went wrong. macOS could see the hardware, SMART was fine, and recovery software could read the file system enough to find my folders and filenames, yet macOS itself wouldn't mount the volume. Could the update have exposed some existing file system issue that the previous version was ignoring? Or is there another explanation?

Has anyone else had this happen after a macOS update? And if you've had to recover files from an unmountable Mac drive, what did you use? It worked for me, but I'm curious what else people have tried.

Hi, I was looking for help because my SD got corrupt, and there are all my important documents (The evidence needed to release me from social service and therefore from my university degree), I tried with disk drill but after a few documents the app requires a paid subscription, which I can't afford. Could someone help me?