What you're doing is trying to use WebUpdater to load fw. That might only maybe partially work for a soft-bricked device. Because WU can see devices in preboot it's (perhaps) only letting you "load" (copy) the fw GCD file to the nuvi however the fw file could merely only be maybe getting placed into the nuvi's .System folder. Then on the next successful boot cycle of a healthy working device it will self-load the components of what it perceives as a correct GCD (i.e. right HWID and later version of fw) to the correspondingly appropriate regions of the internal memory. Clearly that can't happen for you because in its present state your device cannot boot fully. If the fw has the same or lower version as/than the existing version or is wrong HWID then even if the device could boot the file is ignored regardless (because wrong HWID, or same version is already loaded to fw regions).

Updater.exe works quite differently to WebUpdater.exe despite the similar naming. The former does not just "copy over" a fw file like the latter, instead it directly flashes the appropriate regions from the components of an RGN file. So, for a bricked device that can access preboot we use it to flash a Cure fw RGN file. You should now make the correct RGN file and flash it following the method in initial post of the Cure3 thread, here: [Only registered and activated users can see links. ].

7) If you don't know HWID get it by Use program G7ToWin to retrieve your HWID

Have done this and I get Unit ID 3914635044 ID 1947 software version 8.80, it will also only communicate briefly while in preboot mode then goes offline
G7ToWin can hold preboot only as long as the device is programmed to do so, if it then drops out after giving the info on-screen there's no problem anyway. You have indeed got the wrong file and can thank your lucky stars that you couldn't flash it as it might have then become HARD-bricked. US/EU 25x9 can have two HWIDs and you've downloaded the file for HWID 1759 when your device is HWID 1947, the C4 version board. Read this [Only registered and activated users can see links. ] by Butters for more details and a link to the C4 GCD.

So now download the correct file "nuvi25x9C4_880.gcd", remake the cure RGN with GarminCure3.exe and flash as explained in kunix's thread to re-enable MSM so you can remove the faulty map IMG file you downloaded. Don't forget the important final step of re-flashing the original fw in preboot.

As for the microSD, if it can be seen in Disk Management but not Windows File Explorer it likely only needs to be re-allocated a drive letter then re-formatted. If it's not even detected in Disk Management using a known-good card reader, then it's likely seriously corrupted and maybe irrecoverable. Google for "HDDGURU HDD LLF Low Level Format Tool" and use it if Disk Management can't successfully reformat your card.

Post again if you need more help.