KeePassXC and Signal are regarded as security products. Joplin is not, and I doubt the developer wants it to be. If we push for every product developer to bake their own security systems, we will end up with half-baked products and half-baked security. If people want better isolation between apps, they should choose an OS that does so, or push for one if it doesn’t exist.

If you don’t mind I am curious to hear your reasons. I personally agree with the developer, I think it’s a lot of work and doesn’t provide a meaningful win. If an attacker has access to the system, there are many other ways they can access your notes even if the notes are encrypted at rest. Based on the thread it sounds like what people actually want is isolation and access control, but I don’t think that responsibility should fall on the app developer, it should be handled by a broader system (like Veracrypt, or Flatpak).