Is it possible to divide a 40m² apartment into two units?

In my last message I already wrote that in case of a rental only the room with kitchen is rented out (e.g. to an (exchange) student, while the other room remains free for the owner.

What is the point of that? How do you want to rent to someone (long-term) who basically only gets one shared apartment room and the other room is unused. Conversely, if you use the empty room (for what? – secret trysts with your lover while your wife stays home to look after the child?) and want to use the toilet, suddenly someone is sitting on the pot... Since we don’t know your motives and splitting into two apartments is not possible, you can’t expect a reasonable answer here either.