Qrzysio

This plugin converts every uploaded JPG or PNG image into modern WebP format to improve performance and reduce file size.
Key features: 
– automatic conversion of JPG and PNG images to WebP on upload 
– correct generation of all WordPress image thumbnails 
– configurable WebP quality level 
– optional maximum image width (original images are resized before thumbnails are generated) 
– automatic removal of original JPG/PNG files to save disk space 
– full compatibility with WordPress “big image scaling” 
– automatic alt text generation based on the filename 
– filename sanitization and collision-safe renaming
All settings apply only to newly uploaded images. Existing media files are not modified.
<h3>Configuration</h3>
You can configure the plugin in Tools → Force WebP.
Available options: 
– WebP quality (0–100): controls compression quality for newly uploaded images 
– Max width (px, optional): limits the maximum width of original images before WordPress generates thumbnails (0 = disabled)
All settings affect only images uploaded after saving the configuration.

Force WebP

Say goodbye to JPG and PNG – make your site run on fast, modern WebP images.

kristarella

Copy or convert terms between taxonomies.
Taxonomies include categories, tags and any other custom taxonomies that may be present with your active theme and plugins.
This plugin, based on Categories to Tags Converter, allows you to copy (duplicate) or convert (move) terms from one taxonomy to another or to multiple taxonomies, while maintaining associated posts.

Taxonomy Converter

For starters, the plugin has deprecated code and produces errors on PHP7. Looks like the code hasn't really been touched all that much in many, many years.

The biggest problem is that when the terms are converted, the term descriptions are removed.

Doesn't include term descriptions

Copy or convert terms between taxonomies.

Force WebP vs Taxonomy Converter