Hi,
I want to add “In Stock” and “On backorder” to the product filter.
I tried a lot of plugins but none of them worked.
In fact, I do not want to use the plugin because it can be done with a simple code.
Stock management is enabled in Woocommerce > Settings > Product tab. On backorder is configured in the product page. If you mean a label, our theme does not have any options. You can search a custom labels plugins
The default Woocommerce does not have such an option, unfortunately. Our theme does not have such option either. You will have to find a plugin or customize.