s7 has the flat plug... NOT the C-version. these are available from the S8 or S8+ onwards, but they don't work for me because the protective cover is thick and the charging part doesn't reach into the C-opening...

How is the question to be understood? Do you mean because of USB C-A / USB C-C?
USB C-A is on the dock USB-C is on the other end of the cable (the "normal", flat USB plug).
The USB C-C variant then only fits computers or laptops that also have a USB-C port.

It is a universal docking station. It is not device-specific. It fits many mobile phone models with a USB C connection.