Chadder - Encrypted messaging app
Crypho - End-to-end-encrypted messaging and file sharing
GrapheneOS - GrapheneOS is an open source privacy and security focused mobile OS with Android app compatibility.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Earlynote - A time-travelling messaging app
Confide - On the off chance that you need to get your messages private and encoded then utilize Confide that will fill in as your own and classified courier.