Lacie Hard drive not recognized by Mac ( latest software version) help

You need to go through a process to determine what might be happening.

• Check the USB cable to determine if it is connected. Try changing the cable if possible.
• Under Finder, open Finder Settings. In the window that opens, confirm that External disks is checked to be displayed.
• Check to see if the Mac "sees" the disk. Open About This Mac under the Apple logo. Click More info.... On the left side of the opened window, click on General. At the bottom of the window, click on System Report. It is there that you can see everything that is connected to the computer. If the disk is not reported to be connected you likely have a failed disk.

I'm having a similar issue. I followed your steps and going to the System Report, I found my external to be showing. Happy that it's not failed but not sure what to do next. Do you know what can be done to make it appear in Disk Utility so I can use First Aid on it?

Just to give an update because I solved my own issue. When I saw that my external was showing I plugged in another external and it came up as normal. After a moment, the lacie too showed up, I've no idea why but it's happened again a couple times and doing the same thing of having systems report opened and plugging in a new drive worked. ¯\_(ツ)_/¯

You ran Disk 1st aid on that drive???

Boot into Restore mode,CMD+r keys...

Look at top of screen for Utilities menu...

In Disk Utility>View, select Show all Devices, highlight the top left entry.

Run Disk First Aid on all items in the left panel, from top down.

Connect it to a PC and reformat the drive with the free DiskGenius app. After that, connect it again and see if it could see by Mac. You need also check if there are bad sectors and health condition of the drive.