I created an external volume with macOS High Sierra. When I try to convert it to APFS with Disk Utility, the "convert to APFS" is greyed out. I tried unmounting the volume first, then it's not greyed out, but when I try to convert, I get this error: The operation couldn’t be completed. (com.apple.DiskManagement error -69546.).
I heard that having "cloned" a volume may prevent it from being converted to APFS. I don't remember if I cloned it or not. I created it with El Capitan, then upgraded it to High Sierra. Now it won't convert to APFS.
Any way to do the conversion? such as terminal command or something?