I noticed that the services wickedd-dhcp4.service and wickedd-dhcp6.service are not running. Should I enable them? And I remembered that I could not connect some years ago with older KDE versions. But this was the fault of the KDE's NM UI. Maybe the old problem is back? https://bugs.kde.org/show_bug.cgi?id=209673 Also I rememberd a problem with the WIFI N mode https://bugs.launchpad.net/ubuntu/+source/linux/+bug/575492 I will try that too. But I tought that these problems were all resolved with newer KDE/NM/Linux versions. What do you think?