Can't install on external HDD

I want to install and use Garuda linux (Gnome Ultimate) from an external HDD for which I need to install EFI partition in internal HDD (due to restrictions created by bios ) and Root partition on external HDD but the "next" button is not enabling on setting these options. Can you please make some appropriate changes so that I would be able to install the OS on external HDD.

What changes would those be?