Okidoki, thanks for your reply 
EDIT #1 :
DISCLAIMER :
This part is for Qt developers (me not belongs there) and for very curious peoples (gotcha! ) 
Anyway,
I turned to DuckDuckGO in Webpositive URL field as searched for
set DBUS_SESSION_BUS_ADDRESS
I got an answer – highlighted by the web search engine
on the right side,as a simple command line
How to export DBUS_SESSION_BUS_ADDRESS
http://stackoverflow.com/questions/41242460/ddg#41244272
I’ve finally found the answer, running the following command exports the output of dbus-launch:
export $(dbus-launch)
–User55412
However I checked the Stack Overflow - the first finding URL - too.
After I tried out.
~> export $(dbus-launch)
~> env| grep DBUS
DBUS_SESSION_BUS_PID=89094
DBUS_SESSION_BUS_ADDRESS=unix:path=/tmp/dbus-xYV3QP5wB1,guid=b92a0c16a98f4e10234605e067782c19
~> find /boot -name qdbusviewer
/boot/system/lib/Qt6/qdbusviewer
~> /boot/system/lib/Qt6/qdbusviewer
qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""
~>
It had worked, the Q-DBUS Viewer could connect to dbus,
… however a plugin was not found, so further error messages I got
when I tried to select enlisted entries
I was fullfilled, no more minutes I would spend on this topic and Qt tool … it was enough to find out a “HOW TO …” for me about Q-DBUS Viewer program.