You could… Take your rule one step further…
rule "Alle Lichten ann/uit"
Item Lichten_ann_uit received update
gLight.sendCommand(Lichten_ann_uit.state) // This will pass whatever state your "Lichten_ann_uit" is in to your gLight item
If you have programmed a series of Velbus Actions between buttons and Velbus outputs, why do you need to monitor it and mirror those actions with openHAB commands.
What I meant by suggesting Groups, was that you can use the Group items within HabPanel / BasicUI/ ClassicUI etc, they behave just like sliders, switches etc
Try adding the gLights switch to your UI and see what happens.
If you use the Default condition for a Group Switch, if ANY of the items it is linked to is ON, the Group will show as ON, but if they are ALL OFF, the group will show as OFF.
You could use this status indicator as a quick way to see in your UI if everything in your house is switched off.
Next useful bit of information.
You can link Switch Groups to Dimmer items, because Dimmers report ON, OFF and %, so the group will react to the ON & OFF states.
Again, I find this all much easier with PaperUI, but hey it’s not everyone’s choice.