Are reservations even possible? I wouldn't worry much about availability, especially in 1st class.

(That train is operated by Vy Norway and thus should be on Entur. If the chat doesn't work is there an email or call number?)

This is what their website says when I look for the connection:

You can't make a seat reservation on that route as far as I know. Just come to the station like 10 minutes before the departure to be amongst the first to board the train. 

We took that train a couple of days ago. We also understood that reservations were not possible, but someone came on board at a later station and claimed our seats !!  So it is apparently possible to book a seat, though I think there are very few that do that.

The train is operated by Vy and was a noisy bumpy ride, not something to look forward to. 

According to Entur reservation is only possible if you buy an ordinary ticket….not for interrail pass holders…

Are reservations even possible? I wouldn't worry much about availability, especially in 1st class.

(That train is operated by Vy Norway and thus should be on Entur. If the chat doesn't work is there an email or call number?)

This is what their website says when I look for the connection:

 

This is the Formats on vy website

thats we I want to make a reservation. But according to Entur Chat it is Not possible for interrail pass holder, only when you buy a ticket