Thanks for using Notezilla .
In the version you are using you will find an option called "Sort checklist" which actually orders the list by Not done followed by done.
This option "Sort checklist" wasn't named correctly so in the latest update, have changed to "Sort by status". Yes a shortcut key for sorting would be good. I will take note of it.

In future updates, I will change it so that only the done items are moved to the bottom without sorting the whole list.