WEBP to JPEG Converter

It looks like all the WP image conversion plugins go the other way ?? You could try a general internet search for “bulk convert webp to jpeg”. It is possible to custom code your server’s built-in image editor to do the conversion. Most commonly the editor is GD, but some use ImageMagick. Example GD conversion is shown in this SO topic: https://stackoverflow.com/questions/59621626/converting-webp-to-jpeg-in-with-php-gd-library