Is there a way to make taskbars and vwm to communicate to each other, such that the taskbar only contains the programs that are active in the current window of the vwm? In a similar way as altdesk does it for instance. As for now, I guess they are just two seperate modules. That would be great.

Yes, ckVWM, RabidVWM can do this. Read docs and your personal.rc file.

If there released a modified vwm which takes advantage of it, Tasks is able to do this another way.

I posted already a reply which has not yet appeared. Discard it , sth new to me is that the personal.rc file has priority over other.rc, and there VWMHideTaskOnSwitch was set to false. Now it works! Thx

Getting there, getting there...