I’m not sure I understood your question, so please correct me if I’m wrong. As of today, you cannot change the extension of a file with Strapi. However, there are other solutions:
- Use a NodeJS package like Sharp (https://sharp.pixelplumbing.com/) to change your images before uploading
- Use an online converter like Squoosh (https://squoosh.app/) to manually change it
On the front-end, styles may not help much after the photo is uploaded. However, you can change the format before uploading it by using the canvas in JavaScript. Refer to Uploading Canvas Image to a Server for an example.