Doesn't Ubiquity have this functionality? I think part of the problem though is setting up the servers, which can be a bit pricey. Not many people have NASs, despite them becoming much cheaper and easier to set up. It is hard to compete with the simplicity of cloud platforms. A full home operation still requires you to have the drives stored somewhere.

I think the better solution is that someone offers a relatively cheap service that has a cloud option that fully encrypts the data and uses e2ee for communication to the server. Though it is hard to prove that you don't own the keys (I mean how many still distrust Signal?).