Before I try to go through the hoops of reporting this as a bug, I would like some feedback to see that this is not my own stupidity.
Edge 93 is on my machine returning en-US formatted numbers and dates with the nb-NO locale.
(123456.789).toLocaleString('nb-NO') returns '123,456.789'.
(new Date(2012, 11, 20, 3, 0, 0)).toLocaleString("nb-NO") returns '12/20/2012, 3:00:00 AM'.
Chrome 94 and Firefox 92 return the correct '123 456,789' and '20.12.2012, 03:00:00'.
It's almost as if Edge doesn't recognize the BCP47 notation nb-NO for Norwegian Bokmål. But variations like nb, no, nob, and even nn-NO, nn, nyn (for Norwegian Nynorsk) don't return the correct result either.
Yes, you are right. I did a simple test on the content you mentioned and found that it does have such a problem, but I think you don’t need to worry about it. Because this issue has been resolved in future version of Edge, you will know if you try to test it in Edge Canary. Result in Edge Canary:

So I think you could look forward to the new update of Edge.