5G WLAN: Where are the other channels?

I just bought a RT-N66U and updated its FW to 270.26.

When I go to the Web GUI and configure a (static) channel to be used in the 5 GHz band, I only see channels 36, 40, 44, and 48. I wonder why the other channels, e.g. > 100, do not appear on the drop-down list.

Any hint for enabling the remaining channels is appreciated.

I'm located in Switzerland, Europe.