aa-globe

This plugin has no settings. 
Just activate the plugin and check if sold out items have moved to the bottom of the list.

Catalog Sorting by Stock Status – In Stock First, Sold Out Last

This plugin changes the sorting of a catalog (or product category) so that out-of-stock items are always at the end of the list

tierrainnovation

Smart Category Ordering is a plugin that allows you to sort your post content (per category). You can apply your sorting to a single category, or have your settings follow a category tree, covering the parent and children categories.
When sorting by “Smart Title”, that option is there to the leading ‘a’, ‘an’ or ‘the’ from a post title when sorting. This is the only difference between “Smart Title” and “Title.”

Smart Category Ordering

Allows you to alphabetize categories by post title, by trimming leading text, by post date.

Catalog Sorting by Stock Status – In Stock First, Sold Out Last vs Smart Category Ordering