Last March c’t tested some alternatives https://www.heise.de/select/ct/2021/8/2106310351115657652

    App        Security    #users    ease    Functio-   Price
              & privacy    Germany  of use    nality     
    Element      o           -        -         o        Free
    Signal       +           o        +         +        Free
    Telegram     -           +        ++        ++       Free
    Threema      +           o        o         o        $3-$4
    Whatsapp     o           ++       +         +        Free
    Wire         +           o        -         -        Free
    
    ++ very good     + good    o good enough    - bad