Seeing it takes a flash to region 14 to update the main firmware it seems that there's no corruption in that part of the flash memory at least.
Provided the Rufus format actually leaves the visible memory genuinely empty, I suggest you try this: Set your computer to show all hidden and system files, [Only registered and activated users can see links. ]. Remove everything from the visible file system keeping a backup copy. Manually create a folder named Garmin in the root of the empty memory and then boot the eTrex ignoring and clicking through any warning messages. If it completes the boot, shut it down and connect to computer again to check if there's a newly-created file GarminDevice.xml or GarminDevice.temp in the Garmin folder.
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