A hosted Linux VM synchronised with a local server at your home and/or office might be the type of solution you’re looking for; a system where you’re paying for (and managing) the end-to-end solution and using open source technology so as not to depend on a proprietary provider or on a private entity shutting down.

You could also control the type of encryption being used.

In terms of local server, you could use something like an Intel NuC so it’s low power and a very small form factor.