Lemm.ee has horizontal scaling, and afaik it’s the only lemmy instance to have added it. He has a sticky on [email protected] that talks about how he’s using a half dozen different servers to split the load, although there’s a few services that can’t be split like image caching, so they just get their own server. I think the changes are being pulled into future updates so hopefully other lemmy instances can start doing the same
Yeah, they all download files in a proprietary format so you can only watch using their app, it’s not just a .mp4 that you can use whenever