Like anything US based the risk from government is not so much technical correctness but the risk that they (or Google or Apple or whoever distributes the app)

Like anything US based the risk from government is not so much technical correctness but the risk that they (or Google or Apple or whoever distributes the app) could secretly be compelled to do something like distribute a version of Signal that exfiltrates private keys or messages, perhaps based on specific criteria, w/o the user's knowledge. On top of the risks inherent in the underlying platforms (iOS, Android, etc.). Signal also does not think that warrant canaries pass legal muster. But it's still probably the best option. And if you're concerned by those risks I think building and auditing the public source code instead of relying on app store distribution would mitigate.