No Wifi Connection via wicked on minimum installation with X environment. 

I was able to resolve this locally by downloading following packages from 

https://download.opensuse.org/distribution/leap/15.5/repo/oss/x86_64/

iw-4.9-1.17.x86_64.rpm
libnl3-200-3.3.0-1.29.x86_64.rpm
libnl-tools-3.3.0-1.29.x86_64.rpm
net-tools-deprecated-2.0+git20170221.479bb4a-3.11.x86_64.rpm
wireless-tools-30.pre9-150400.13.6.x86_64.rpm
wpa_supplicant-2.10-150500.1.3.x86_64.rpm

installed via 'rpm -i <package.rpm>'. Some of these packages were already present.

I don't know which package / combination of packages resolved the issue but after this step the installation / wicked could make the wireless connection. 

It appears there is one or more packages missing in the minimal installation option for Leap 15.5 to let wicked establish a wireless connection.

For reference (in German):

https://www.opensuse-forum.de/thread/66976-kein-wifi-auf-leap-15-5-nach-minimalinstallation/