BRIAR is excellent, it can be downloaded from F-droid, I've been using it recently, trying to find a really private and encrypted application for my messaging. the largest number of opinions and reviews were for "Threema" but before paying. Look for an open source and free-to-use solution.

The top options that I found in my opinion would be these: Threema.
BRIAR.
SimpleX.
Session.
Signal.