OK that at least means you have a valid backup that wont Brick you should you need to restore, has the SD been in heavy Use (alot of Writing(freeshop, FTPserv, SD Management) did you get it online from something like eBay/Amazon (a 3rd party seller not a verified by Amazon as it can happen but rarely from them) have you used it frequently to copy data on/off to via a USB SD Adapter (regardless if this a microSD or full SD form-factor plays no role in when flash memory just cant take it and bites the dust)
if you got your SD from an online source not direct from the manufacture,(or thru amazon but a non "Fulfilled by Amazon") proper local store that isn't some drugstore/"Ma 'n Pa" store higher chances you got a Fake SD and it started to overwrite itself. this makes me think more so w/ the second screenshot as not everything was restored (you can count your "Nintendo 3DS" Folder as a total write-off as there's no way to be certain even if restored digital signatures are intact or files themselves are not corrupt. (sorry but more than likely your saves are Toast.)
GM9/your 3DS isn't at full fault. as
@Majickhat55 stated that at the time of reading it couldn't read anything properly due to a Corrupted (in this case of Fat32) FAT Table or full on partition/FS and it has-to to complete the process write garbage back. this garbage write w/ a corrupted fs/partition can even endup writing this gibberish as the FAT (think of it like a big File index but thats over simplifying things and a discussion for another time) causing what you see in the first Screenshot.. If it had written the garbage to the partition Table you'd just get back in windows "This drive needs to be formatted" (as to windows any unknown/unsupported Filesystem/partition scheme gets seen as a unformatted (unknown File system) or uninitialized Disk (unknown partition scheme) and the 3DS in all aspects wouldn't be recognized as i believe the 3DS only supports Fat32.
please check your SD with this:
https://3ds.guide/h2testw-(windows).html this wont be the 100% sure fire answer to your problem as it could just be bad timing (incorrect handling of the SD, mishandling/manhandling it. and random Corruption) if you sadly have a Fake SD there's nothing that can be done save for just buying a new one. if you do Test the SD immediately when you get it home, and if proven fake (again proper retail stores have a verrrrry minute chance of also getting fake sd cards in stock.) (Walmart is scummy like this and does it a bit often than people give them credit for.) take it back for a refund and just buy directly from Sandisk or such. at the end of the day w/ a new card make regular backups if your SD 's Data, so if this happens again, your not caught with your pants down and so much progress Lost.