Debian (fdisk) doesn’t support creating a partition with more than 2TB due to using the MBR partition table. You’ll need to use GPT instead:

sudo apt-get install parted

# Check the disk you want to format
sudo fdisk -l

# Replace /sdx for the disk you want to format
sudo parted /dev/sdx
mklabel gpt
quit
sudo parted -a optimal /dev/sdx mkpart primary '0%' '100%'

Now you can format the partition with the file system you want:

sudo mkfs.ext4 /dev/sdx1

You should be able to replace the mkfs.ext4 command with mkfs.exfat if you want that file system (see section below )

Which partition type to choose?

As a rule of thumb:

• Use ext4 if you plan to use the disk only on linux.
• Use exFAT if you plan to share between multiples OS. Linux, Windows and MacOS support it.

Debian out-the-box does not support exFAT. You’ll need to install fuse:

sudo apt-get install exfat-fuse exfat-utils