ext4 vs EXFAT: Storage size difference

I have 2 hard drives, one is EXT4 and one is EXFAT. Both are 8TB, and both contain the same files.

However, if I look at the amount of space being used in Gparted on Ubuntu, there is a big difference. Also included screenshots from the File Manager in Ubuntu.

EXT4: There is 154 GB free.

EXFAT: there is 13 GB free.

From the screenshots, it looks like both drives have a allocation unit size / block size of 512 bytes, so I don't think (?) that can explain it (could be wrong though).

What gives?

The EXFAT cluster size is not 512 bytes, which explains the difference.

Microsoft's Default cluster size for NTFS, FAT, and exFAT has this table:

Your cluster size is then 128 KB, while for ext4 this is likely 4 KB bytes.