Well, I'm sorry to hear about that. You mentioned the 4T Seagate external hard drive does not show up on the desktop and you receive the error message when you try to mount it in Disk Utility, which reads Could not mount "disk2s2". (com.apple.DiskManagement.disenter error -119930868.)
Here, we offer you two methods to fix this issue.
Method 1: Force mount the drive using Terminal. You need to unmount your drive in Disk Utility first and then go to Launchpad > Other > Terminal and double-click to open it. Type in 'diskutil mount /dev/disk2s2' and press Return to run. Then, restart your MacBook and unplug-replug your drive to check whether it shows up on the desktop and can mounted successfully in Disk Utility.
Method 2: Format your Seagate external hard drive. Your drive is blank, so you can format your drive without performing data recovery.
- Open Disk Utility and select your Seagate external drive from the sidebar.
- Click Erase.
- Set a name for the drive and choose a format for it.
- Click Erase
If you have any data in your drive, you can use iBoysoft Data Recovery for Mac before reformatting.
- Free download and open iBoysoft Data Recovery for Mac.
- Choose your 4T Seagate external hard drive and click Search for Lost Data.
- Preview and choose the file you need and click Recover.