That looks pretty much identical to my Vaillant's motherboard Ecotec plus 831. Your model designation suggests its not a UK model?
My extension bridge is connected to the ebus terminals ( two wires) and the taco modulated the boiler too.
I have read if the boiler is recent a couple of years old that the taco can't communicate with the boiler over the ebus interface, Valiant changed something.
Apparently the newer Vaillant VR66 controller module speaks a different dialect of eBus protocol which Tado do not yet know how to process. The older VR65 module is compatible with Tado.
If you're in the Netherlands you will probably have a VR33 module which translates the eBus protocol to OpenTherm which Tado also understand.
Unfortunately in the UK at least Vaillant regard fitting a VR33 module as invalidating the warranty even though it is a genuine Vaillant part.
It might be worth posting a message to Tado asking for support for the VR66 module as the more people who request this the more likely they are to work harder on solving this. (Vaillant themselves are unlikely to help.)
@jelockwood It was on one of your posts a I read it 👍️