This appears to be a ubiquity-only bug. It doesn't appear in either Subiquity or Calamares - tested in a VM with an external USB drive attached. The USB drive appears in Grub, which is to be expected, but the installers don't attempt to install to it.
Unless there's some flavour that I'm not aware of still using Ubiquity, could this bug be closed?
This appears to be a ubiquity-only bug. It doesn't appear in either Subiquity or Calamares - tested in a VM with an external USB drive attached. The USB drive appears in Grub, which is to be expected, but the installers don't attempt to install to it.
Unless there's some flavour that I'm not aware of still using Ubiquity, could this bug be closed?