GUID Partition Scheme with Catalina

I have a Seagate external hd and when I connect it and try to use SuperDuper to copy to it, it tells me I need to convert it from APFS and that I need a GUID partition scheme. But in Disk Utility, the partition icon is greyed out and I see no other way to create a GUID partition scheme. When I click on erase, it lets me select the format of Mac OS Extended Journaled but there is no dropdown field to select scheme.

So I'm stuck. Any idea how I can make this external hard drive play nice with SuperDuper on Catalina?

i have read a previous reply to this, which says to click on the parent drive. This does not help. The partition icon is still greyed out.