Help Image Manipulation Class

How To rename extension that use Convert() method ?

my code below does not automatically rename file extension 

PHP Code:

        
        $img = $this->request->getFile('image');
        $newimage = $img->getRandomName();

        \Config\Services::image()
            ->withFile($newimage)
            ->resize(1360, 768, false, 'auto')
            ->convert(IMAGETYPE_WEBP)
            ->save(FCPATH . '/img/');
        $img->move(WRITEPATH . '../public/img/');

        dd($img->getName()); 


My output file name still jpg/png
I need webp extension output filename.
Please help.