What is the path to the theme directory containing webp files?

Ok, so I’ve got this plugin working nicely. When I convert the contents of my /uploads/ directory, the webp images are saved to /uploads-webpc/

What is the output webp folder for theme folders? I have many images in the themes folder, and I’ve converted them successfully (I tested the front end and i can see they’ve been converted) but i cannot for the life of me find where these webp images are stored in the wordpress directory. They’ve got to be somewhere… but where?