No idea why the SSD isn't listed as a boot option. The only thing I can think of is that the BCD on the 4TB drive isn't configured properly, or the boot files didn't get copied properly to the EFI ...
When you plug in your USB drive, do you see a UEFI NTFS partition? Do you know why Windows Explorer is displaying such a partition? If not, then you are at the right place! That partition usually ...