I’m actually not really sure. Webp definitely helps reducing the file size.

For me, the small preview window is animated but when extending the image it needed some time to work. But this might be caused by the image being hosted on catbox.

I assume lemmy has to host the file directly.

This file is not hosted on lemmy, or at least that’s what I assume. I don’t really know how direct image posts with URL work in lemmy.

But all of this probably depends on the UI you’re using (web version / alternative web UI / mobile app etc.) and could also change with future updates.