enable legacy boot (bios) vs uefi

my default inspiron 7540 uefi boot, does not show all my drives. I want to be able to change the boot order.

can't really find a post anywhere how to provision how my uefi to show all drives like in so many uefi examples, my default only shows my hdd, no dvd, no ssd, no usb

Just like this.https://www.dell.com/community/Inspiron/enable-legacy-boot-bios-vs-uefi/m-p/7423808

external devices in Legacy mode, also not use. how to boot external device in legacy ? I have disable PTT, secure Boot. and switch to ACHI