Have you installed a battery driven zigbee or Z-Wave wall switch that is compatible with Hubitat? I.e. a wall switch that you could stick to a wall without any cables any where you like. If so, which one did you choose?
It is. 868 MHz in the EU. Zigbee is the same frequency world wide.
Also, in-wall gang boxes are of different sizes in the the EU and North America. Therefore, even though you want a surface mount device, the ones we use in North America will not match the size/appearance of the other switches in your house.
I don't know what shipping would cost, but it's worth noting that Zooz has started making EU versions of some of its products. I don't see one for the ZEN34, above, but I do see one for the ZEN37. Aeotec almost certainly would have something, too (like the Wallmote or Nanomote), being where they are based, but I don't know their European offerings as well.