Lumo currently requires a Lockdown exception to work (not just sync conversations, but to work at all) when iOS is in Lockdown mode. Even if I generally trust Proton, seeing a non-essential app tell me that it needs elevated privileges to work with my security configuration is exactly the kind of behavior users have been taught to be suspicious about.

Apple is also broadly encouraging users to turn on Lockdown (https://tech.yahoo.com/ai/apple-intelligence/articles/apple-sends-spyware-alerts-users-212400627.html) to defend against spyware. Some of those users may get scared into enabling Lockdown mode without knowing what an exception is, how to manage it, or the technical reasons for it. But if they're familiar with other secure apps like Signal, they will wonder why Lumo can't store encrypted chats in Lockdown but Signal can, and they'll be confused by the conflict between using a secure, privacy-focused app with a device setting that they enabled for security and privacy. This is both a usability and an optics issue.