This HOW TO assumes you have the knowledge to execute commands from a terminal window on the Raspberry Pi desktop or over an SSH connection.
This HOW TO will walk you through updating the bootloader, verifying the boot order, coping the SD card image onto a USB SSD drive and finally booting from USB. The Raspberry Pi 4 comes with an EEPROM that supports USB booting. Author: Raspberry Street Press HOW TO: Boot Raspberry Pi 4 from USB SSD Drive February, 2021