There's a way to hide read messages, but not deleted ones? Reproducible: Always
This is a feature I also find myself wishing for. My ideal UX would be for deleted messages to be "collapsed" in some way that still makes it apparent that there are some deleted-but-not-yet-expunged messages there.
Trojitá is no longer maintained, please switch to a maintained alternative like https://apps.kde.org/kmail2/ Sorry for the inconveniences.