I've tried a lot of very functional clients. I suppose you think of Element? There's also Cinny, Hydrogen (both web), Fluffychat, Nheko, gomuks. Maybe quaternio

I've tried a lot of very functional clients. I suppose you think of Element? There's also Cinny, Hydrogen (both web), Fluffychat, Nheko, gomuks. Maybe quaternion is more to your taste? Not sure if it supports E2EE.