Hi Felix,
thanks for the reply!
I also found this connection now.
Now I also know why the Ny-App shows replacement busses on the Oslo-Trondheim-Route. They seem to transport bikes but unfortunately they are already booked out the next couple of days.
So my plan now is to take the ferry from Hirtshals to Bergen (I’m in Skagen right now) and then ride north and just see how it goes.
This, of course, just postpones the problem with the train ride to the return but hopefully I’ll be able to book that one earlier than just 3 days before.

Really looking forward to the trip but I’m also a bit scared. Let’s see.