Hell yeah, I think I managed to solve my troubles. I managed to find a suitable card reader initially to make a backup image of the SD card, but then decided to take a look at it using all the tools I had at my disposal, namely the Windows Disk Management console and MiniTool Partition Wizard. The first simply reported the drive as RAW and so was of little use other than to tell me that it has a single partition spanning the entire card as far as I can tell.
This was peculiar, as from what I'd gathered, SD cards formatted as internal storage should have two partitions. At this point I felt somewhat defeated, that the SD card had entirely given out. But I was still after my data so continued digging. I was still hopeful it was just some kind of FS failure that scanning the drive for errors would correct once I found a way for Windows to recognize the drive as a valid volume.
The SD card suddenly damaged question reminded me that I too have MTPW installed. I poked around and realized it does see the card properly as a FAT32 partition and can even explore its contents. I scanned the drive for errors. It did find some, so first I took an image backup of the drive as is, then run the FS check again allowing to correct errors this time. Immediately Windows has started to recognize the drive and it appears all contents is intact. Then I turned off my Android device, inserted the SD card and powered it on. This time it didn't present me with the "there is a problem with the SD card, pick your poison" notification, and even apps installed on it appear to be working.
IDK how come I didn't just lose all the data I desperately wanted to save given from all the research I'd done the feat should be impossible from the technical standpoint due to the supposed encryption of the card. But alas my tablet is special, because even when used as internal storage, the SD card can be accessed as is. I even in desperation inadvertently would have destroyed the encryption key had it been actually generated because once I learnt I need a rooted phone in order to extract it I unlocked the bootloader w/o realizing all the implications.
Since my question was about the initial reason it came up damaged, I guess I need to include the FS scan log:
The type of the file system is FAT32.
Volume Serial Number is 0403-0201
The \ entry contains а nonvalid link.
Windows is verifying files and folders...
File and folder verification is complete.
Windows has made corrections to the file system.
No further action is required.
15 437 824 КВ total disk sрасе.
32 КВ in 1 hidden files.
10 336 КВ in 323 folders.
4826 720 КВ in 1 118 files.
10 704 КВ available.
32 768 bytes in each allocation unit.
482 432 total allocation units оп disk.
331 272 allocation units available оп disk.
