This is the official information: https://avinor.no/en/airport/oslo-ai...nsfer/transfer (see non-Schengen to non-Schengen).

As far as I know, there's only security between land-side and air-side at OSL, and that will require going through immigration. Security is efficient at OSL, immigration not always so. But I believe this only will involve neither.

It says you need to go through security again. Security is efficient, but it will probably require immigration also, and that might take longer time, depending on the passport (Schengen /non-Schengen)

This post and thread has further information: https://www.flyertalk.com/forum/35373144-post101.html