External hard drive with Catalina

is this an error message or are you suppressing the external drive appearing on the desktop in Finder>Preferences>general

does the drive appear in Disk Utility?

Macintosh HD (whatever you named it}/Applications/Utilities/Disk Utility.app

how is it formatted?

videomanR Said:

“External hard drive with Catalina: I upgraded to Catalina and since then unable to use my external hard drive...it is not recognized but when i use sierra it all ther”

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Using Disk Utility:

1. Using First Aid in Disk Utility:

Run Fist Aid in Disk Utility and see if it shows a corrupted hard drive. Boot into Recovery Mode select drive name along the left and click First Aid along the top. Run it and see what is reported.

2. Mounting the Drive in Disk Utility:

• Disk Utility in MacOS:

If mounting it in Terminal is of no success, use Disk Utility. Open it using Spotlight Search: Hold down [command + spacebar] and type: Disk Utility. Click on the drive and select Mount along the top.

B. Disk Utility in Recovery Mode:

If that cannot be done, mount this in Recovery Mode. Hold Down [command + r] upon boot. Select Disk Utility, and mount the drive. Click on the drive and select Mount along the top. Reboot the Mac and log in as an administrator, seeing if it is now seen and accessible.

It sounds like the disk is not mounted. In Disk Utility when you select that volume is the "Mount" button active?

If that doesn't work try this:

Launch/Utilities/Terminal and copy & paste this command at the prompt:

diskutil list

Press return.

If it sees the disk, note the number of the disk (far left column) you want to mount.

Then, copy & paste this command:

mount /dev/(number of disk)

Put in the number no parenthesis.

Press Return.

Also might try

mount force /dev/(number of disk)

Is your external drive formatted at APFS or Extended Journaled?

Same question about your internal drive.

I believe the external drive needs to be Extended Journaled.

OK. I what way is it not recognised? Does the disk not show on the desktop? Does it show but you can't open folders on it? Does Time Machine say the drive is not connected? etc.

Go to Finder > Preferences > General.

Make sure “Hard disks” and “External Disks” are checked.

Does that help?