Having a USB startup enabled me to launch the official Libreelec image on the 4B 1.4 model from a USB storage device without any problems. This image does not work with an SD card (u-boot is not suitable for this model). This way you can no longer depend on having the correct u-boot as part of any image and run different images from any models, as long as there is support in the kernel for the image being run. 