I have a full working proficiency in Norwegian. I had some Swedish at school and lived a year in Denmark before moving to Norway, so I can not claim to have started from nothing, though. I already had most of the grammar down before starting with Norwegian. That said, here are the tools I used:
- Duolingo has a strong Norwegian course.
- Anki has a deck of sentences, mostly from Tatoeba, with a few mistakes, but overall okay quality.
- Clozemaster has courses for Norwegian bokmål from English and French from bokmål. I used it actively for a time.
- I read news at NRK, the Norwegian public broadcasting company.
- I participate in and follow discussions around my interests in Norwegian; for me, roleplaying games. I started by listening a podcast and started understanding some at around episode 15 or so, I would guess.
- Of course, I also live here and use the language daily with acquaintances and at work.
The Duoling course is quite good. Most of the other resources I have used build on Tatoeba, which lacks an active Norwegian contributor and therefore has some bad sentences there; so one needs to be critical about them.
I did not use the NTNU course, but NTNU is a highly respected university in Norway, so their course is likely okay.
But even more important than taking a course is actually starting to use the language. Whichever activity you normally do online, try to see if it is possible to do in Norwegian, at least a little. It will be impossible at first, and do not worry about understanding, but you will get exposed and used to the language. Maybe study a bit first, though.