So it is there at least. But has filesystem errors. Probably badblocks…
Is the block device there?
file /dev/sdb1
If it is a broken superblock, then repair with a backup superblock:
Since you use encryption, you have to unlock it and use the unlocked mapper:
sudo cryptsetup luksOpen /dev/sdb1 root
Instead of /dev/sdXY you use /dev/mapper/root
If the drive has badblocks, then I have bad news…
Since you use encryption, I would not recommend using
sudo fsck -vcck /dev/device
which would commonly used. Probably the readonly check would be better, since encryption don’t like random writes…
sudo fsck -vck /dev/device
See also here for more information: badblocks - ArchWiki
In any way mount the partition read-only and save your data somewhere else just in case. Then you are at least safe.
sudo cryptsetup luksOpen /dev/sdb1 root
sudo mount -o ro /dev/mapper/root /mnt