Your referenced blog post was actually my starting point before hitting the issue.
And it doesn't work on EliteDesk so I starting trying to simplify the problem and make boot more standards compliant, if this was the issue.
Blog post implicitly uses HP laptops (BCU settings syntax is a bit different between desktops and laptops) and desktop and laptop BIOS seem to use different implementations so I think problem is desktop specific. I don't currently have any EliteBooks at hand for comparison. I'll try to get a few to lab.
So far I've tried a few other manufacturers systems (mainly Lenovo) and they work fine with the same process (format to GPT, change BIOS config, reboot). Both plain FAT32 boot as in blog post and ESP partition method work.
Only EliteDesk doesn't boot UEFI disks after boot mode change. It just doesn't seem to check at all if disk has any boot files and I can't even tell BIOS manually to boot to local hard disk.
SCCM and OSD TS are a red herring. I'll put together a repro without SCCM but plain WinPE to better illustrate the problem.
