I have set up Raspbian on a USB device using the method described here:
https://www.tomshardware.com/news/boot- ... 39782.html
and also seen in several other places.
I have installed rpi-eeprom, but found that the EEPROM was not updated on reboot.
I tried updating manually, but got the error message "BOOTFS: "/boot" contains no .elf files".
I assume that the update program is looking at /boot on the USB device, not the SD Card.
I ran rpi-eeprom -h, and found the following comment: "If /boot does not correspond to the boot partition on the sd-card and this is not a NOOBS system then the mount point for BOOTFS should be defined in /etc/default/rpi-eeprom-update".
Its not clear to me exactly how to define the mount point for the SD mount, and I don't want to experiment with the EEPROM update process, given the potential to corrupt the EEPROM and/or operating system.
I think the safest option would be to make a separate SD card based raspian system just to update the Pi 4 EEPROM, and then swap back to my "work" SD card.
I would appreciate any comments.