Cannot format new external USB hard drive to APFS

iMac running OS 11x, Disk Utility, Toshiba USB external hd, SuperDuper to backup internal hd.

I am helping a friend do a complete backup of her main hd using SuperDuper. The external Toshiba drive is new and comes with a PC format, so the drive doesn't appear in SuperDuper when I launch it. I need to format the drive using APFS to perform the backup. I launched Disk Utility and erased the disk, then looked on the drop-down menu for APFS but it wasn't there. The only Mac formatting options were using the old file system. In the menubar, the "format for APFS" was greyed out.

I tried rebooting into Safe mode and tried again with Disk Utility but got the same results. I took the new hd home and tried on my Mac mini/OS 10.13.6 but no joy there either.

How can I format the disk to the new Apple file system to use it with SuperDuper to make a complete backup?

Please help.