Good news for those who may want to boot from other than SD card. There is a new change out for doing just that.
Y'all might want to check out this article in the Raspberry Pi documentation. Allows your boot EEPROM to be updated changing your RPI 4B to boot, say, from the network! Or a USB device when such code becomes available. Here is abridged details.
Raspberry Pi 4 boot EEPROM
The Raspberry Pi 4 has an SPI-attached EEPROM (4MBits/512KB), which contains code to boot up the system and replaces
bootcode.bin
previously found in the boot partition of the SD card. Note that if abootcode.bin
is present in the boot partition of the SD card in a Pi 4, it is ignored.
Network and USB boot
Support for these additional boot modes will be added in the future via optional boot loader updates. The current schedule is to release network boot first, then USB boot.
Recovery image
If the Raspberry Pi is not booting it's possible that the bootloader EEPROM is corrupted. This can easily be reprogrammed using the Recovery image available on the raspberrypi.org downloads page.