So the key appears to be this question in the installer, which must be answered No:
If left to “yes” (the default), SCALE 25.10.0 fails to boot from either the Transcend 128 GB NVMe stick or the Patriot P310 240 GB one–the system sees no available boot devices and drops me into the UEFI shell. If set to “no,” it boots successfully from both devices.
So this is looking like a pretty strange result: to boot SCALE from NVMe on one of these boards, you have to disable UEFI boot; to boot CORE, you have to enable it.
But then the boot option to boot SCALE appears as EFI OS. Weird.