erasing external hard drive

FWIW, you do not have to be in Recovery Mode to erase an external drive.

See: How to erase a disk for Mac - Apple Support

Make sure to select "Show All Devices" from the Disk Utility "View" icon then select the top level of the external drive.

mri1397 Said:

“erasing external hard drive: i am trying to use disk Utility . i am erasing an external hard drive that is formatted APFS . but when i try to erase it, the only choice is APFS. Suggestions ?”

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Use Disk Utilities in Recovery Mode:

Boot into Recovery Mode, and see if you can format it in Disk Utilities that way.

Be certain to Mount the drive first, erase the Drive, then Format it.

You are welcome.

NTFS, I'm sure is what you mean. There is no "NTFC" partition type. So, use a PC and see if you can format it using it. That is why using a PC it is a success for NTFS partition-creations. Using third party-apps to format it might be an option, though.

For example:

Partition Magic is/was a great program for managing partitions. It was discontinued in 2009. Regardless, if you have an older computer, you could use that software for creating partitions. It might work on a Virtual Machine, though. Virtual Machine programs are VMWare Fusion and Parallels. Basically, a Virtual Machine is "Windows-in-a-window."