You're trying to mount an entire disk, but that disk has an msdos
partition table with*no* partitions.
There are several problems here:
1) An msdos partition table only supports disks up to 2 TB and yours
is 4 TB.
2) You didn't create any partitions.
3) You didn't create an exfat file system, either on the raw device or
on a partition.
My advice would be:
1) Put a GPT partition table on the disk instead of msdos.
2) Create a single partition that spans all the usable space.
3) Create an exfat file system on that partition.
After that, you should be able to mount /dev/sdb1 wherever you like.
An alternative path would be:
1) Create an exfat file system on the raw device (/dev/sdb).
2) Mount /dev/sdb directly.
I don't think this is wise, simply because it may lead to surprises
in the future, when you forget that you've done it this way, or when
someone else tries to use this disk and expects it to have partitions.
However, it*is* a choice that you could make.