Perhaps niche compared to the entire web, but we use lossless webp for gaussian splat data delivery for realtime rendering. (https://developer.playcanvas.com/user-manual/gaussian-splatt...).

Scenes often comprise gigabytes of lossless webp, some of which you can see at https://superspl.at.

We could get better compression using a custom encoder, however with webp the browser decodes off the main thread, copies the resulting data to GPU memory and caches the images for us. All very useful on the web!