All rail travel by train is included in Norway, except the Flåmsbana and Flytoget. But for Flytoget there are plenty of alternatives with the Vy trains (R10-11-12) to get from Oslo Gardermoen to the centre of Oslo. These local trains are all included in the pass.

For Flåmsbana you get a discount as well (of +/- 25%), Flåmsbana is also included in the Norway in a Nutshell tour, as are some parts of the Bergensbanen (usually to Voss, return from Myrdal) which can be done with an Interrail pass.  Maybe you can get a discount for the Nutshell tour, or maybe you’re better to use your pass on the railways, and buying ordinary bus, Flåmsbana and Ferry tickets. I’m gonna try to find some information about that.

Long distance trains in Norway need to be reserved, which you can do by chatting/calling https://entur.no/

And maybe you can ask if you can get a discount with your pass, for the Norway in a nutshell tour. The wisdom of the web says it’s possible, but information is a bit dated and fragmented. Better ask Entur too, or somewhere at the counter once in Norway. Since that tour is basically nothing more than a set of (rather expensive) tickets with public transport, I’m sure it can done cheaper by buying the bus Voss-Gudvangen, the ferry Gudvangen-Flåm, and the Flåmsbana (with pass discount), and using your pass for the ordinary railway rather than buying the Nutshell tickets seperatly.

But you should calculate a bit for yourself if it’s all worth that hassle :)