I wish there was some kind of small, soundless video supporting transparency for emojis, stickers, small animations, diagrams in slide shows, etc, that is guaranteed to autoplay and loop without issues.
The problem with <video> of course is that there's no way to tell if it's going to play an annoying sound, take a long time to load, change the screen brightness due to HDR features, require a weird proprietary codec, need the browser to render video controls, and so on. So they end up getting blocked from autoplay by default.
I suppose APNG or WebP are ideal for this but it is poorly supported, in that very few tools let you export to APNG or WebP --- browsers actually have decent support for this [1] and Discord uses APNG for stickers.
[1] https://caniuse.com/apng