Electricity meters in Germany calculate the electricity consumed according to the Ferrais principle (VDE-AR-N 4400 standard). This means that the generation and consumption across all three phases are added together with the correct sign, for example: Ptotal = 250 W + 125 W - 175 W (production by photovoltaics) = 200 W.
Currently, however, the electricity generated is only related to the phase on which it is fed in.
My function request is that there is a function in the energy dashboard to be able to reproduce the energy meter as accurately as possible using the Ferrais principle.
You are speaking about Watts (power) while the energy dashboard is about power Wh). So your question does not apply to it. The energy dashboard does not have the values you speak about, so it is impossible to grant your request.
The energy dashboard needs a Wh or kWh sensor, and that should be doing the right calculations.
You can always create a helper or template to sum values that you can feed into the energy dashboard or other places. So what you ask (once understood what you need to use) is already possible.
But be aware that adding Wh sensors together is possible, but is not the same as calculating Wh from added W sensors. That is because values vary over time. Tht is why what you ask is impossible for the energy dashboard to do the way you want it to.
TLDR: it is up to your smart energy meter integration or other power meter integrations/calculations to get you the values you need. They should calculate preferrably separate import and export values for the energy dashboard to consume.
In the Netherlands I believe we use the same principle, and my smart meter returns the properly calculated values that I can feed straight into the dashboard.