nintendo

I watched the entire video you linked (7min+), and it seems the save data are all back after he rebooted the system.

Here are what happened in the video:

He was playing Pokemon Sword and suddenly the game crashed
He couldn't reopen Pokemon Sword and the system asked him to redownload
He tried to redownload but it said there were no enough space
He checked the storage (games and saves), and apparently there was plenty of space left
Many of the game saves were shown to be 0MB
He rebooted the Switch
The system said his SD card couldn't be recognized and asked to format the SD card, which he declined
The Fit Ring software mysterious appeared as the first title on the screen, before Pokemon Sword
He tapped Pokemon Sword icon and initiated the download again
While it was downloading, he went to check his game saves, and all the save files are still there (of varying sizes raining from several MB to several hundred MB)
He checked his album but everything after 7 month ago were missing. (I suppose the missing ones were stored in his SD card)
The video ended