This thread is mistakenly marked as an Accepted Solution: I am experiencing the same obstacle to getting basic "boot from a flash memory at power-on" functionality with a Stream 14 purchased 3 weeks ago and none of the suggestions offered here help. Also, the original poster, Bignickmel never confirmed that anything offered here solved his problem.
I am seeing that: at power-on, after typing ESC until my fingers bleed, I can go to F9 and successfully boot either from the installed Windows 10 or from a Legacy USB flash memory (bootable Linux in this case); but, if I go into the BIOS and move the "USB Diskette on Key/USB Hard Disk" boot option to the very top of both the UEFI and Legacy boot list, the power-on default continues to be the internal SSDrive (Win 10.) So, I'm right back where I started, having to manually intervene with F9 to boot from USB flash and I want to emphasize that the problem is not getting it to boot from flash - it's getting it to boot from flash at power-on. It's all about boot order.
The "Item Specific Help" on the right half of the BIOS Boot Option screen gives no hint about what it takes to make the BIOS chose my Legacy USB bootable flash as the first boot device. All it tells me is that with Legacy support enabled, the "UEFI boot order has a higher priority than the Legacy boot order." Huh!!? Are they trying to say that all the UEFI boot options take priority over the Legacy boot options? Does that mean that only a UEFI USB flash can be made to boot at power-on? Or, do you need to force the internal SSDrive to become a Legacy device so that a Legacy USB flash can be moved above it on the Legacy list and get chosen at power-on? They don't provide enough information. And, this isn't out in the weeds somewhere. This is the year 2019 and people EXPECT flashboot functionality to come with a laptop that is in no way shape or form a Chromebook, as has been suggested by some at HP. You shouldn't have to get into a wrestling match and arguments over warranty support related to external hardware to make that functionality happen.
The "SmartFriend" department at HP claims to know the secret trick to make this Stream 14 do what every other computer does without a fuss ...but there's a catch: they want you to pay them money before they'll be your "friend" and reveal the secret trick - their justification being that their BIOS doesn't need to have basic functionality since the bootable USB isn't an HP product and they're happy to stonewall you with this! They also claim that the secret trick is freely available somewhere on the HP website (they won't say where) and this thread (#5764547) proports to answer exactly this question so it appears to be the only possibility. Except of course, this answer doesn't work at least up to this point.
So, I don't know what's going on at HP these days, but perhaps this frank description of my recent experience may help you the understand the situation. Any accurate insight or workable answer you might be able to offer will obviously be appreciated.