XenForo is able to optimize images (including, but not limited to, attachments and avatars) by converting them to WebP format on upload. You can choose to store either the original file, or the optimized (WebP) file.<br />
<br />
If you wish to optimize existing images, you can do this from within the <a href="admin.php?tools/rebuild/">Rebuild caches</a> page after you have enabled this option.<br />
<br />
<strong>Note:</strong> Optimized images will not load on certain <a href="https://caniuse.com/webp" target="_blank">older browsers</a> such as some Apple systems released prior to September 2020.