G7ToWin only reads modern devices that are in preboot and also Windows Device Manager only shows them under "GARMIN Devices" when they're in preboot. Therefore for the ~30 seconds the logo splash screen is showing it's actually in preboot and can be flashed using Updater.exe to load correct fw as an RGN file. BTW, SD text commands cannot be used because the device needs to be getting much further into the boot cycle (after "loading Maps" appears on screen) before the card is recognized and Ldr.bin initialized.

So you should simply load an RGN file (named 097201000630.rgn for safety). To make that file use RGN_Tool to convert the GCD file to RGN. Post again if you need further help in that regard.