Still not accessible on mobile
Why is that? It should be accessible, isn't it?
The Norwegian course is in beta, which means the current launch is a "test" version where users are trying it out and reporting any errors. Whenever a new course begins beta testing, it is first released to the website, as multi-platform support is a recipe for more errors and extra work for those involved in creating the course (both the course's volunteers and the Duolingo staff). Once the course becomes more stable, as measured by the average number of reports per 100 users, it will be released to the apps via an update. Based on previous courses, it should take a few weeks before the course is released to the apps. I think the most recent beta launch, Turkish for English speakers, took around a month to become available on them.
In the meantime, you can access the course on your mobile device through your web browser. There's a mobile version of the site that looks very similar to the (iOS) app and supports languages as soon as they're released to beta. You can also switch to the desktop version (while still on your mobile browser) if you'd like to help out the course creators by reporting errors (the report a problem button isn't in the mobile version of the site), but it's a bit clunkier to use. Just be sure you're checking for updates for the app so you can get the course on your app as soon as it's available.
Hope this helps!