Group: Forum Members
First, if you're using 64-bit Windows 10 on your system, which I assume you are if the system is that new, then you shouldn't be using 32-bit Windows PE. That adds a needless complication, but more importantly 64-bit is required for booting in UEFI mode, and if your system boots its normal OS in UEFI mode, you should also boot your Rescue Media in UEFI mode rather than Legacy mode. Not only is it more convenient not to have to switch modes when you want to use Rescue Media, but the Rescue Media's "Fix Boot Problems" works differently based on how the Rescue Media was booted -- so if you boot in Legacy mode, it won't run the correct boot fixes for an installed OS that you'll want to boot in UEFI mode.
In terms of getting your USB device to boot, are you trying to accomplish that by going into the BIOS to muck with the boot order or are you accessing the system's one-time boot menu option? You should be doing the latter on a UEFI system. Temporarily attached USB devices won't show up in the BIOS Setup's boot device list of a UEFI system. You mentioned that you did a clean install of Windows 10 on this system. Did you achieve that by creating Windows installation media on a USB flash drive and booting your system from it? If so, what happens if you build Rescue Media to that same flash drive and try to boot your system from it the same way? It should work the same way since the Windows 10 Setup environment runs on WinPE 10, just like Rescue Media. Granted, Windows 10 1809 Setup would run on WinPE 10 1809 rather than WinPE 10 1709 or 1803 as you would've used for your Rescue Media, but that shouldn't make this level of behavioral difference.
If your USB device doesn't even show up in the one-time boot menu while UEFI is enabled, then try another flash drive model and/or other USB ports on the system. I've seen flash drives that for some reason can't be used as boot devices at least on certain systems, and I've seen systems that will only boot from certain USB ports.