Hi
Can Radxa check to incorporate u-boot/ u-boot SPI changes to boot from USB first?
Please check with balbes-150 since he mentioned it to help boot from USB then micro-sd card easily to try different Linux OS’s easily from USB.
https://github.com/150balbes/Build-Armbian/blob/master/patch/u-boot/u-boot-rk3399-tv/usb-start.patch#L14
Another post of his for booting Linux from USB.