What does the Norway–Portugal tax treaty actually decide?

Three things that matter in practice: who gets to tax each income type (salary, dividends, property, business profits), the tie-breaker when both countries claim you as resident, and the mechanism for relieving double taxation. What it does not do: erase either country's filing requirements or fix sloppy residency facts. The treaty is the referee — you still have to play the positions correctly in both returns.