Intrinsically/semantically no but the expectation is that the texts are encrypted at rest and the keys are password and/or tpm+biometric protected. That’s just how this works at this point. Also that’s the government standard for literally everything from handheld devices to satellites (yes, actually).
At this point one of the most likely threat vectors is someone just taking your shit. Things like border crossings, rubber stamped search warrants, cops raid your house because your roommate pissed them off, protests, needing to go home from work near a protest, on and on.
Yeah but it really shouldn’t be that way. Just add a pin or something, it’s way too easy for people to just grab devices or install malware to leak keys. The current standard for security is that everything is encrypted at rest regardless of whole disk encryption.
Signal is still better that most of the stuff out there but it’s not above well intentioned criticism