I was looking into the documentation and we can read the following:
" Is USB Boot for the Pi4 supported? Is the Pi4 with 8GB RAM supported?
The bootloader for Home Assistant OS (uboot) does not yet support Pi4 booting from USB. Support is likely a month or two away as of July 2020.
The Pi4 with 8GB RAM is now supported on the 64-bit image."
-> Ddoes anyone knows when it will be officially supported(boot from USB/SSD)?