One nice thing about KDE compared to most of the other DEs is that the window manager (kwin) is separate from the underlying components, and it can be replaced!
You get i3 for tiling window management but you still get to use KDE's system settings to do configuration like display settings, themes keyboard shortcuts, etc, just like you did before. You can also pick and choose which parts of the KDE desktop you want to keep (menu, krunner, etc)
Since i3 is just a window manager and is lacking all of that system level stuff it really rounds out i3 to feel like a full DE instead of having to piece together other tools to do those things.