Well, that went not much of anywhere...I did the install to MTD+NVMe, and at boot, the machine came on, the blue light came on, and then never started blinking. I've been using a power supply that came with my Pi 400, but I suspect that does PD. Now to find one that doesn't and is beefy enough to run this machine.
But...the machine does boot from SD after doing the installation to MTD+NVMe with that same power supply. Is it really the power supply, or something else?