Is a bypass valve installed and possibly incorrectly adjusted? So that a large part of the volume flow goes unused from the supply line to the return line via the valve bypass?
Didn't you have a modulating heat pump? It also regulates the flow rate down when maximum power is not required. The flow is modulated down to achieve the optimal temperature difference in the heating circuit for the optimal operating point at the corresponding outside temperature. Theoretically, you can set the control of the HUP in the Luxtronic from automatic to manual 100%. Then you can see what your hydraulics can handle. But this makes no sense for "daily use" because you then have an efficiency loss.
Password for the settings known?
Yes, I did that once, I remember. Then the pump was noticeably audible and the sight glasses showed a much higher flow. But I think the auto setting should have its purpose.
So everything is in the green zone. Consumption is correct, temperature is correct. So what do the sight glasses matter? The heat pump already regulates that for optimal operation.