30GB+ used on freash Arch install+KDE? Why?

Keep in mind that a part of the filesystem will be reserved on creation. Here if I create a completely empty ext4 filesystem with:

truncate -s 230G /tmp/img
mkfs.ext4 /tmp/img
mount /tmp/img /mnt

Dolphin reports "213.8 GiB free of 225.3 GiB (5% used)"