In principle, there are only three clients for Android that are up to date and maintained:
1) Element
2) Schildi Chat, which is an Element fork and only has a few more features. But they don't provide any more security
3) Fluffy Chat, a client written in Flutter that is nice to look at but is incredibly slow. And offers less than Element. Possibly less in terms of security too.
Long story short:
You're really only left with Element, a fork of it, or a slow Fluffy.
All the same in terms of security.
Basically: eat or die
You might get further here too
https://www.kuketz-blog.de/element-messaging-ueber-die-matrix-messenger-teil7/