Yes, answered in my original post... "Tried booting from a cold start, no go". In other words, completely shutdown the machine, plugged in the USB drive, restarted... still no go. I purchased a license x 3 PCs for Aomei Backupper Pro so obviously reluctant to change to different software. It all works fine with every other machine I own (3 in total), just refuses to work on the Dell. Do yourself a favor.... Create a Macrium Reflect bootable USB stick and see if it boots your XPS 8940 from a full power-off. If that works, you'll know it's the Aomei software and not something wrong with your PC. And, it won't cost you anything to try Macrium, since it's free, and easy to use. And if Macrium does boot the PC, contact Aomei for tech support and/or a refund... 
XPS 8940 running Windows 10 Pro 21H1 Trying to boot from USB recovery media created via Aomei Backupper Pro (PE build). The bootable drive isn't listed in BIOS or the F12 boot menu. Tried on two other UEFI based machines and it works perfectly on both. So, logically, I'm thinking it must be down to a specific setting in the XP 8940's BIOS. Booting from USB is enabled, can't see any other setting that might affect this. Tried booting from a cold start, no go. Any assistance would be greatly appreciated.
XPS 8940, unable to Boot from Flash Drive