Not sure if this is at all helpful as information, but I just recently ran into a similar issue with a Godox firmware update on a TT685 speedlight. The Godox TT685 is old enough that it uses the "G1" updater, which requires a 3rd-party proprietary USB driver. Which was written for Windows 7, it's so old. Which means it's not properly signed for more recent versions of Windows 10, and Windows 10 won't load the driver (sees it as a security risk), so the USB connection cannot be made.
To get my TT685 to connect with the G1 updater, I have to boot my Windows 10 box with driver signing enforcement disabled. This involves:
- Hold down Shift while selecting [Start menu]→Power→Restart. Continue holding down the shift key through the spinning circle of white dots until you are in the blue advanced boot options window.
- Select Troubleshoot.
- Select Advanced options.
- Select Start-up Settings. You'll see a list of options and a Restart button.
- Select Restart. More spinning circle before you can select how you want to modify the bootup from the list of options.
- Type 7; to select "7) Disable driver signature enforcement".
You box will now boot up with driver signing disabled and Secure Boot turned off, and (hopefully) the USB driver should work. Once you restart the box, both driver signing and Secure Boot are re-enabled.