The UK has left the EU and the agreed transition period expired 31 December 2020. If you are working in Norway, ensure you have official proof of residency when travelling to Norway.
Also read: Brexit's impact on Norwegian corporations with UK management
You must apply for residency permit as citizens of countries outside the EEA/EU. You can no longer use the special application procedure and type of residence permit as those who registered before 31 December 2020.
You can visit Norway for 90 days without a visa or residency permit, but you are not allowed to work without applying for a residency permit. The 90 days is during a 180-day period.