The Raspberry Pi 4 now supports booting from USB drives

The default eeprom firmware with loader for Raspberry Pi 4 boards has added support for booting from USB drives. Previously, Raspberry Pi 4 boards could only boot from SD cards or over the network. Experimental support for USB booting was has added introduced in May, but it wasn’t available in the default firmware.

The initial lack of USB boot capability and the lengthy implementation process (over a year since the board was released) is due to a significant redesign of the boot organization in the Raspberry Pi 4 and the use of USB through a separate VLI controller with its own EEPROM, connected via the PCI Express bus.

Source: opennet.ru