I was there too because German embassy told me I have to transfer visa to new passport- but after waiting long time at immigration office they siad no transfer possible and they even don’t mentioned anything about stamp transfers - so I also learned it only at the airport:)
No transfer possible keep you old passport visa still valid - just the latest immigration stamp has to be transferred but no need to go to immigration for that when you fly out next time they will ask you to go to a separate counter and they will transfer it ( less than 5 minutes)