Both the mobile and the paper pass have the same validity.

Mobile or paper is personal preference. Here's a comparison of some features.

The Interrail Global Pass is valid in 33 countries like the Scandinavian countries like Sweden, Norway, Denmark and Finland. 

You can buy a global pass as mobile pass on the railplanner app or as paper pass. It is the same. 

You can also buy one country passes, but they are only valid in the select country.

In those countries-which are very advanced- in fact over 70-80% of normal travellers use their fone to store the tickets. Thats what you will see when a conductor comes around. In fact in some big cities like Oslo, the urban transit is now only with fone-tickets! No machines, no finding coins etc. So a mobile pass will not be unusual out of the way. Paper is more likely to be.

Note that in DK there are a few local lines that do not accept passes and in SE there are also competition fast trains STO-Göteborg by MTR that does not.

In general in NO-SE-FI ALL longer distance trains must be reserved, that is fairly easy to do online, but it also means every such trip cost a few € extra. The info that it is optional in the eurail site seems to be no longer the case, as several people have reported here from own experience.

Do you know where to book Norwegian seat reservations online? Interrail can do it but they only have paper reservations for Norway so that doesn't really count.