Turkish railways is one of the operators who don't send all their timetable data to the European Timetable Centre so nobody has them. That means you'll have to enter missing trains manually. If the stations are also missing, enter random stations in the planner, then tap on "Add it manually” and enter the correct stations.

Not just that but it seems (from reports from someone with german sense for exact details and living+working in TR on specialised rail-forums) that there since covid simply hardly any trains are running. Main exception are the hi-speed new lines IST-Ankara/Konya, several local networks around large cities (but some of these are in their own fare-system with cards and do not takes passes) and a now kind of local cherished ´East Expressu´ with cult-status that gets booked out solid as soon as they release new trips (about 1/week), And thats it for now. Since many yrs before 2000 the long-dist BUS is the main means of transport there-plus now for longer the quite cheap and multiple budget-airlines. Ank-Kayseri has a bus at least ev 30 mins-and had 1 train/day (plus on some days 1 extra). Plus that bus only took half the time of train.

IST did have its own stations (istasyonerlerlu) for Evropa and Asya-but that is long gone and these are now standing derelict. A heavy-duty reformed metro-style local railline has been built, also with tunnel to connect and its outer ends have the long-dist trains.

Also check seat61.com-as always-for hints + links.

Using a pass is also very bad value-local tickets are far cheaper as passdays

@mcadv "hardly any” is simply wrong, as has been pointed out to you multiple times. If you have another opinion, then please include links to facts.