Right now I received a helpful hint from Oliver Busse that you can import ICS files not within an action but with the “normal” import function of HCL Notes ( File / Import ) and switch over to Calendar File (.ics ):
After a very helpful hint from a well known friend ( aka “The Wickerl” ) the issue with the wrong date/time in a calender entry only occurs if you forward a calendar entry with a right mouse click and only in the German template !!!
The cause has already been identified and will hopefully be solved soon.