The USB-C connector on the MagWLED-1 can be used for flashing new version of WLED or other firmware. As it comes out of the box, it can be flashed by simply connecting the device to your computer and e.g flash via https://install.wled.me/. In some cases (like a bad firmware that introduces a boot loop), you might be required to hold the BOOT button down while plugging in the device to force it into bootloader / flashing mode.
On some early (summer 2024) MagWLED-1 boards, the USB-C PD negotiation is known to cause interference with the USB connection when connecting it to a non-PD capable USB port. Modern laptops, such as MacBooks and recent Dells work perfectly. Many USB hubs will, however, continuously connect and disconnect the device. So, if you have issues flashing, plug the MagWLED-1 directly into your computer.