I will also answer the question, sorry!

My biggest problems grammatically .. probably gender tbh, it’s very basic but I’m a native English speaker so I think it’ll be many years before it comes intuitively to me. When speaking I’m pretty often catching myself out like ‘’og det var blå.. nei da.. blått mener jeg’’. That and accuracy with prepositions.

My biggest problems have been not about grammar, though. What I’ve struggled with most has been getting Norwegians to speak to me and to not swap to English at any moment. Finding books that aren’t like 700 kr with international shipping. Understanding different dialects. Getting spoken intonation correct... reaching those high notes of Eastern dialects good god. The urge to learn Swedish instead. Kidding with that last one hahaha.