Bridgify may be a good app to have pre-installed also before going to a protest. It’s Bluetooth/peer-to-peer based with mesh network capabilities so you can still message friends (within ~300 feet) if your mobile network is too congested or offline.
Used in Hong Kong protests: https://www.bbc.com/news/technology-49565587
@erwincat Briar is great there’s but no iOS app for now 😞 if everyone in your group is using Android, then yeah, Briar would be good to use instead.
Personal instance of nitrohorse (nitrohorse.com).