Cruise stop in Oslo

You have do your own research. I have no idea what your interests are or your preferences. I could spend time making suggestion you might not like.

Hit the local library and check out travel DVDs, guidebooks, etc., for that location and determines what interests you and your group. Hit the web site for each port. See what is offered. When you get off the ship, head for the nearest TI and see what local tours - walking and otherwise - can be booked. Steves has a guidebook for many ports but not all. And the answer is the same for all your ports. Register with your ship on Cruise Critic.com to learn what other shipmates might be doing.

Each of these Oslo suggestions are easily accomplished on your own. Several are nearby, making for a nice pairing. The Viking Museum and the Norsk Folkemuseum are a five minute walk apart, but they require a ferry ride or a bus ride (a #30 bus) from a stop near the Fortress and city hall. The Viking Museum and the Historical Museum share management, so admission to one is good for the other. Both are excellent although they are not located near each other. The Historical Museum is near the National Gallery and they are both near the Royal Palace.
I like all these places, and I recommend them, but, then again, I really like Oslo.

My top choices to see in Oslo are the Viking Museum and the Vigeland Sculpture Garden, an amazing place.
While out on the island for the Viking Ship Museum, there are several other small museums you can visit there too.

Ditto for: Vigeland Park (200 amazing sculptures) and Norsk Folkemuseum (open air living history museum)

Start with: https://store.ricksteves.com/shop/p/norway-guidebook

Buy 24 hour Oslo Pass: https://www.visitoslo.com/en/activities-and-attractions/oslo-pass/

Check off what interests you: https://www.ricksteves.com/europe/norway/oslo

▲▲▲ City Hall Oslo's artsy 20th-century government building, lined
with huge, vibrant, municipal-themed murals, best visited with
included tour.

▲▲▲ National Gallery Norway's cultural and natural essence, captured
on canvas.

▲▲▲ Frogner Park Sprawling park with works by Norway's greatest
sculptor, Gustav Vigeland, and the studio where he created them (now a
museum).

▲▲▲ Norwegian Folk Museum Norway condensed into 150 historic buildings
in a large open-air park.

▲▲ Norwegian Resistance Museum Gripping look at Norway's tumultuous
WWII experience.

▲▲ Viking Ship Museum An impressive trio of ninth-century Viking
ships, with exhibits on the people who built them.

▲▲ Fram Museum Captivating exhibit on the Arctic exploration ship.

▲▲ Kon-Tiki Museum Adventures of primitive Kon-Tiki and Ra II ships
built by Thor Heyerdahl.

▲▲ Holmenkollen Ski Jump and Ski Museum Dizzying vista and a schuss
through skiing history.

▲ Nobel Peace Center Exhibit celebrating the ideals of the Nobel Peace
Prize and the lives of those who have won it.

▲ Opera House Stunning performance center that's helping revitalize
the harborfront.

▲ Akershus Fortress Complex and Tours Historic military base and
fortified old center, with guided tours, a ho-hum castle interior, and
a couple of museums (including the excellent Norwegian Resistance
Museum, listed above).

▲ Norwegian Holocaust Center High-tech walk through rise of
anti-Semitism, the Holocaust in Norway, and racism today.

▲ Norwegian Maritime Museum Dusty cruise through Norway's rich
seafaring heritage.

▲ Edvard Munch Museum Works of Norway's famous Expressionistic
painter.

▲ Grünerløkka Oslo's bohemian district, with bustling cafés and pubs.

We were on a Baltic Cruise this time last year that included Norway. We found the Rick Steves Northern European Cruise Ports book very helpful for all the ports we visited but especially Oslo. We toured on our own and bought the 24-hour Oslo Pass for transportation & ferry plus venues. We got the pass at the Nobel Peace Center near where our ship docked and then took the ferry to the Viking Ship Museum, Kon-Tiki museum and folk museum. Then took a bus to the Vigeland Park. We then took the tram back to town and the ship. All were covered by the pass. We left the ship and went straight get the pass and then to the nearby ferry. We had no lines and things were not crowded until we arrived at the Viking Ship Museum which was a little crowded but with a pass we didn't have to wait to get in. As said earlier, the book were very helpful as well for Copenhagen, Stockholm, Berlin, St. Petersburg, Helsinki, and Tallinn.