As the UEFI default for USB was to not wait for initialization, that made keyboard input impossible – even to get into the UEFI menu and change the setting.
So I had to take that box apart and disconnect all drives so I could start the machine and have the UEFI be active long enough to do the HID initialization so I could get into the UEFI menu and tell it to always initialize HIDs before bringing up the bootloader.