Are you using the USB-C cable for anything other than doing this update? For example, are you using it to send a video signal to the Spectrum?
The reason I ask is that not all USB-C cables are created equal. There’s plenty of USB-C cables to choose from:
- Passive USB 3.2 / Thunderbolt 3 / Thunderbolt 4 cables that should carry data and video just fine.
- Active Thunderbolt 4 cables that should carry data and video just fine.
- Active Thunderbolt 3 cables that’ll carry Thunderbolt data, but no USB or video signal.
- USB 2.0 only cables that can carry a low-speed USB signal, but no video data.
- Charge-only cables that don’t have any of the wiring needed to carry USB or video data.
I wouldn’t be surprised if there were other variations too. You can’t easily tell what type you have just by looking at the cable.
If you’re using the cable to send a video feed to the Spectrum, it should also be able to carry USB data and should be usable to update the Spectrum.
If you’re only using the cable to do the update, it’s possible that it’s one of the incompatible types of cable. See if you’ve got another cable lying around, such as an old USB printer cable. Others have reported success doing a firmware update over that type of cable. It can just be the type with the square end, not the fancy USB 3.0 end.