16T external WD drive not mounting on brand new Macbook pro

Is this drive connected directly to the laptop?

Make sure to disconnect all other external devices in case one of them is causing a problem.

Does this external drive drive have its own dedicated power supply?

Try restarting the computer since sometimes this is needed from time to time.

Try the external drive while booted into Safe Mode.

When you erased the WD drive....did you erase the whole physical drive? Sometimes external drives ship with odd partition layouts and items stored on the drive which can cause problems. See this Apple article for instructions to erase the whole physical drive instead of just the volume/partition. Also, make sure to use GUID partition scheme.

Maybe the USB adapter or cable has a problem.

Then I found out that Sonoma somehow doesn't support external hard drives formatted exFat,

Not true, but I wouldn’t format a 16TB drive ExFAT.

This didn't solve the issue.

The drive stills doesn't mount.

I can see it in disk utilities, and I try to mount it from there and nothing happens.

It could be trying to pull too much power and can’t mount.

Try setting “allow accessories to connect” to Always Ask, then attache the drive. It should ask. If it does, that may allow it to mount. You can then change the connection setting to whatever you want.

tonycama wrote:

After some more digging it was a security software that was preventing the drive to mount.

So I changed the setting and now it works as expected.

Was it a built-in macOS security setting or associated with a third party app?

FYI, anti-virus software, cleaning/optimizer apps, and third party security software are not needed on a Mac. These types of apps usually cause more problems than they solve because they interfere with the normal operation of macOS. macOS already has great built-in security especially when combined with the user practicing safe computing habits as outlined in this excellent article written by a respected forum contributor:

Effective defenses against malware and other threats - Apple Community

Thanks for the update & follow up. I'm glad you were able to figure it out. Great job of troubleshooting!

I forgot to include a link to the Apple article with instructions for erasing the whole physical drive:

Erase and reformat a storage device in Disk Utility on Mac - Apple Support

Hi tonycama.

how did you fix the security software that was preventing the drive to mount? (i guess I have the same issue here)

thanks