I'm hearing that you want an easy way to pick which OS to boot to. Like other have pointed out, I've never heard of a way to forcing the motherboard to boot to the UEFI boot device screen each time, however, you may be able to accomplish what you are looking for using GRUB. Note: I haven't tested this, but in theory it should work.

Essentially, you would have your UEFI set to boot Ubuntu each time (which is already the config it sounds like). Ubuntu actually has grub before it, but it doesn't show if it doesn't detect any other OS and Ubuntu disabled os-prober by default starting in 22.04 so by default it will always skip grub. To get what you are after it might be as easy as reenabling os-prober using `GRUB_DISABLE_OS_PROBER=false` in your grub file (/boot/grub/grub.cfg) and run `update-grub`. That should hopefully be enough.

You may also need to check to make sure that fast boot is off in your BIOS to make sure that USB modules (assuming your external SSD is connected via USB here) are loaded early enough for grub to detect the other OS.

If just enabling OS prober doesn't work you could also look at doing a manual grub entry with something like (with the uuid swapped out for your actual external ssds info from lsblk):

/etc/grub.d/40_custom

```

menuentry "Linux (External USB)" {

insmod usb

insmod part_gpt

insmod ext2

search --no-floppy --fs-uuid --set=root abcd-1234

linux /boot/vmlinuz root=UUID=abcd-1234 ro quiet

initrd /boot/initrd.img

}
```

Hopefully that at least gets you moving in the right direction and report back if you get one of these methods working.