Backflow prevention - Where / what / exactly how?

I am currently a bit confused. It is about the topic of [Rückstausicherung]. Our architect has planned a floor drain in the basement and now tells me that this will be more expensive because she recommends [eine Rückstausicherung]. So far so clear. However, since we wanted to secure the entire house drainage against backflow, the question arises for me as a layperson: My idea was to lead all drains to the sewer, combine them there, and then install the backflow protection there as well. Our architect now told us that normally the "critical" drains (i.e. basement) are secured against backflow, but the rest are not (depending on the location of the sewer). If we combine everything and only install one protection, we should discuss this with the excavation contractor also regarding the price. How do you see this? What would be more advisable? If I read the plans correctly, the invert of the wastewater sewer is at 286 m above sea level. The top edge of the basement floor is at 287.225 m above sea level. The plan is to route all drains (except the floor drain) through the basement walls. The house drains would then be about 1.5 m above the sewer. The floor drain about 1 m above the sewer.