A normal couchette comprtmt has 6 beds-but perhaps this TCDD/Turkish car onle 4. IF you want it all for yourself, you also have to pay for the places that remain empty-otherwise other travellers can booked in. And even that is no 100% garantee-the railway is allowed to sell the empty space to others if there is an overflow of passengers-you will in the end get reimbursed for that-with luck +patience
There will still be much faster, cheaper and a bit less comfy direct buses between the 2-probably fewer though as the many pre-covid.
Not finding what you're looking for?
Don't be shy and let us know about your challenge.