Thumbnail format doesn't apear on REST API on image upload

I want to generate .webp image formats on image upload and keep the original image format.
When I make direct modification in /node_modules/strapi-plugin-upload/services/image-manipulation.js everything works as expected. All breakpoints and thumbnail formats images generated and linked on REST API.

But when I copy Upload.js and image-manipulation.js to the extensions folder, there is no thumbnail format of the image on REST API. However, all thumbnails are in the upload folder.

// extensions/upload/services/Upload.js

...
- const { bytesToKbytes } = require('../utils/file');
+ const { bytesToKbytes } = require("strapi-plugin-upload/utils/file");
...
// extensions/upload/services/image-manipulation.js

...
const resizeTo = (buffer, options) =>
  sharp(buffer)
+   .webp()
    .resize(options)
    .toBuffer()
    .catch(() => null);
...

// on generateThumbnail and generateBreakpoint methods

      return {
        name: `thumbnail_${file.name}`,
        hash: `thumbnail_${file.hash}`,
-       ext: file.ext,
+       ext: ".webp",
-       mime: file.mime,
+       mime: "image/webp",
        width,
        height,
        size: bytesToKbytes(size),
        buffer: newBuff,
        path: file.path ? file.path : null,
      };

What am I missing?

System Information
  • Strapi Version: 3.2.5
  • Operating System: Windows 10
  • Database: sqlite3 (latest)
  • Node Version: 14.15.0
  • NPM Version: 6.14.8
  • Yarn Version: 1.22.5