Thank you for your replies!
@ase11: You have to install either via antergos-kde-setup (didn’t work for me) or install plasma-desktop. Then I would uninstall everything gnome-related, because in my case gvfs is eating a lot of resources. I think some applets of the cairo-dock are also not working anymore, because I uninstalled gvfs, but the Plasma desktop gives you a lot of alternatives.
@joekamprad: I now switched to SDDM login manager, because you can configure it in plasma settings
The breeze-gtk theme worked well except for missing shadows of windows, but I already created another thread for that.
@Bryanpwo: Okay, in the thread he says that KDE has improved, but the difference for me is just unbelievable. My laptop now runs faster and cooler than with any other desktop environment. On Cinnamon, GNOME or LXDE my processor used to run around 50°C when idle. On KDE it runs at 35°C !!! when idle. That is cooler than my friggin’ blood brah! On Cinnamon I was experiencing BT connection problems - gone! I was having memory problems, being that the longer I used Cinnamon, the more memory was used for cache. I had to hit Alt+F2 and type “r” to reload Cinnamon and I got free memory again. This problem is gone as well. I have no idea why there is such a big difference. I am guessing that Cinnamon just runs well on Mint. I have never had problems with it on MInt.