Why Are USB Drives Not Recognized on macOS High Sierra 10?

The USB drives not being recognized on macOS High Sierra issue can be caused by a slew of reasons, poor connection, unchecked External disks option in Finder, incompatible file system, macOS 10 error, and more. You can fix the issue by checking the connection, selecting the External disks option in Finder Preferences, formatting the drive file system, or reinstalling macOS.

Check the connection. You can try a new USB reader, adapter, or cable to connect your drive and the device. Or, insert the USB drive into another Mac computer to see if it can be recognized.

Check the External disk option. You can launch Finder to see if the External disk option is selected: Finder > Finder Preferences > Sidebar > External disks.

Check the drive file system. Windows NTFS formatted drive is not fully supported by macOS and it is mounted in read-only mode on your Mac devices. You can check the file system of the drive by right-clicking it > Get Info > Format. If it is NTFS formatted, you can format the external hard drive on Mac to make it fully supported by your device.

Reinstall macOS. If you ensure the drive works well on other devices and its file system is compatible with macOS, then I guess there is something wrong with your macOS. In such a case, you need to reinstall macOS on your device.

Hope this answer helped you out of trouble!