Well, video streaming was AFAIK pioneered by porn sites, though not necessarily pornhub, but it could be seen as a representative

The only Desktop one that comes to mind is Interstellar, but you could probably also use a web fronted that is instance independent like phtn.app (Which I would recommend if it works)

They do advertise direct export, but I’m not sure if that means encrypted json

Proton does this as well, you can use it completely offline without an account