Employ the handy all-powerful Terminal, which always comes forward with solutions for difficult problems.
Fixing an external hard drive that’s not showing up on Mac
Console shows if an external drive or any error is detected under the Errors and Faults tab. If no errors show up, then the problem is not caused by the device. To sum up, there are lots of potential solutions for a Mac not reading an external hard drive. If we were to pick one, Disk Drill seems to be the most well-rounded, offering plenty of customizations and power in an easy-to-use interface. Start with the basics: Check whether the drive is properly plugged in. Faulty cable.
Try connecting the same device with a different cable. Damaged USB or flash drive port. It could be a hardware issue with the Mac. Reboot your Mac. Hopefully, some data damage that can be fixed by restarting. Or press and hold the power button and, when a dialog box appears, click the Restart or press R. Incorrectly formatted drive. Not every external drive is optimized for Macs. It could be that you are trying to connect something only fit to interact with Windows devices. See if the external drive shows up here.
For more information, go to the same menu option, then select System Report. Mac not formatted to display external drives on the desktop. Even if that is the case, the drive will still appear in the left-hand column of the Finder menu under Devices.