Hello rini's mom
Firstly, good day and welcome to the SBB Comnmunity.
You are trying to book a train whose departure is months in the future. No local would ever bother booking a train ticket months before. Usually, trains are available for booking 3 months ahead of time, no longer.
Due to planned construction, the timetable has not yet been confirmed.
We suggest checking availabilities with either ÖBB or Nightjet at a later stage.
Kind regards,
Roland