@ScottCE9 I did something different with my Raspberry pi 4:
Raspberry Pi 4Firmware update
Install Raspberry Pi OS on a SD card and boot. Update the OS, which will update the firmware as well (do it via terminal).
Flash the SSD with the Recalbox
Mount the ssd on your pc and change an option in a file named cmdline.txt in RECALBOX partition:
Install the SSD on your NesPi 4 case and enjoy!
Hope that works for you too! 🙂