the save is dead so dont bother haha.
Let me find an old backup from couple of weeks ago and i test doing restoring that one. i update this post with result
EDIT:
Sorry took a while to find emergency backups lol.
Either way:
Checkpoint_01000A0000000012.nsp
Sd/switch/checkpoint.nro
Same error i added two pics of the errors in question.
Restoring save + error = no corrupt save file at all.
Creating a new backup = succes message + freeze or error code depending on my switch mood lol.
After reboot the newly created save + old backup is available. but new the save file is 0 bytes/empty/corrupt.
to be safe i tried three sd cards (256, 128 and 64 GB) didnt change and after that a 16 GB fat32, no luck.
https://imgur.com/a/wJMTk9y (pics of errors if thats even useful for you )