How or with which app do you currently operate your house? You wrote that you don’t want an additional app or rather one for everything. That would be the visualization of the KNX system, that’s what it’s called. The "pure" KNX works autonomously without any displays or apps, meaning there has to be an instance "on top" for nice graphical control via app or touchscreen, right?
Sorry, I completely lost sight of the post... Currently, I don’t control the house at all yet, as we are still in the expansion phase. Visualization is done with the Gira X1. We have meanwhile also made a decision (had to make one) regarding the door intercom system. A Gira G1 is centrally placed in the house, which brings the doorbell and the video from the Doorbird to the G1 via a VPN connection and SIP. We basically only need the Doorbird app when we are out of the house. Our electrician is open to quite a lot, but he initially wanted to tell me that G1 and Doorbird wouldn’t work – but it does, just not via the X1, and some fine-tuning is necessary. It’s also clear that if the router is offline, the doorbell won’t work because no signal reaches the G1. But this risk is worth it for us not to have to install a separate video station from Doorbird. The G1 costs about 1k and the Doorbird indoor video station around 400€. So for 600€, we basically got the complete, central house control on top, which was worth it to us after all. So, although we didn’t get the "jack-of-all-trades" solution, we are satisfied with this solution.