Hello Thiemeawoi31
I was able to speak to the SBB department in charge, also thanks to @Nicole_B .
When reserving seats online, it is no longer possible to choose a zone (business / family) or to select a specific seat type (aisle, window). The system automatically allocates a seat, preferably a window seat.
The entire seat reservation system was replaced beginning of 2024; the online interface is not yet fully functional. The SBB Mobile app will, at a later stage, again offer the possibility to choose the seat type (aisle or window). When this will be possible is not known yet; they anticipate a solution where passengers can choose their seats from a seat map.
If you want to reserve a seat in a specific zone (business / family), this is only possible at the travel office, or by calling the SBB Contact Center: 0848 44 66 88 (CHF 0.08 / min, waiting times may occur. From abroad: +41 51 225 78 56 (24/7).
Kind regards,
Roland