This is DeltaChat desktop client but not with the default Electron. Compile instructions for Debian, Arch Linux and openSUSE. One Linux distribution has this packaged : NixOS, package name kdeltachat-unstable. The software developer is also active in the DeltaChat forum. Posting this here to give this project some more attention cause it would be nice to see less Electron and more Kirigami (or Tauri ?).
I guess I’ll have to try and compile this on Ubuntu because I’m curious what this looks like (and the project doesn’t appear to have any screenshots). Deltachat always had a relatively nifty UI so I wonder what difference going native makes in terms of look and feel.
In my experience, KDE applications look a tad wonky on Gnome, so it’ll be interesting to see how well this’ll integrate compared to the Electron version.