in systems i've seen with severe encryption, the data is only unencrypted by the actual processing engine. otherwise, its encrypted at the field level, during transit and at rest. yes, you have to trust the processing engine isnt doing anything nefarious, but at some level you have to trust something. proton has a solid history of trust despite the one idiot that works there.
youre not smelting your own processors for example. if youre not forging your own processors then youre just not secure!