Thanks for your kind replies!
Currently the Volla X23 is out of stock, I do not know yet, if I will risk to buy a Gigaset GX6 ending up with a phone with Android only.

What about open a new group for devices of the german manufacturer "Gigaset". And in this group open a new sub-forum " GX6"? It seems to me that the hardware is comparable to the Volla Phone X23/X23E?