portable western digital my passport now appear in the disk utility

jacc65 wrote:

I connect the portable hdd nothing in the disk utility

What year model iMac running which macOS version..?

see > https://support.apple.com/en-us/108054

Are you connecting the WD PassPort directly to the iMac or thru a USB Hub..?

Is this a brand new or an older WD Passport external drive..?

Also the External Hard Disk may not have adequate power if it’s BUSS powered. It may need its own power supply.

You might have to turn the setting on

See the devices connected to your Mac - Apple Support

If this is an Apple-Silicon-based Mac notebook, you may have to "approve" new USB and Thunderbolt accessories.

Allow accessories to connect to Mac - Apple Support