Un-hanging the HP Envy 17-DA0013dx for OpenBSD

I recently acquired a lightly-used HP Envy 17" laptop, model DA0013dx, and of course wanted to run OpenBSD on it. It came with Windows 11 on an internal NVME drive. Booting OpenBSD from a USB device failed fast: it hung. To get there, first of course I had to disable "secure boot" in the BIOS.