Why Can't I Use a Pool with IX Application child Dataset and SMB Share in Dragonfish?

zfs rename WD\ Red\ Pro\ 16TB/Dropbox WD\ Red\ Pro\ 16TB/Dataset/Dropbox

or as @DjP-iX said

zfs rename WD+Red+Pro+16TB/Dropbox WD+Red+Pro+16TB/Dataset/Dropbox

create the dataset first in the GUI or via CLI and escape the spaces the same way:

zfs create WD+Red+Pro+16TB/Dataset

This is also a very helpful comment, pay attention to that.

Or you rename the pool first