Hi I have a Ender 3 with the 4.2.7 board, the SD slot is broken, I’m trying to update the firmware Via the USB, I use Cura to send print files via windows and the USB which works fine, Cura needs a Hex file not a bin file is this something that is possible.
The easiest way to fix this is to replace the SD card slot on the mainboard. That requires some fairly good soldering skills, possibly a hot air station.
Another good solution is to build an Octoprint/Octopi out of a raspberry pi. There is a mod to octoprint that lets you update the firmware via the Octoprint/Octopi device. In all honest, this device is the best way to get access to your 3D printer via your home network.