Danish cuisine is not limited to smørrebrød!
For the best current suggestions, I would ask your hotel for recommendations - you could even contact them in advance.
We ate at these restaurants in summer 2023 - so check current reviews. I wouldn't post these as my experience isn't recent, but will since you are getting no specific suggestions: a starting point, perhaps!
These aren't necessarily "close" to the Marriott as in a block away, but Copenhagen is flat and walkable. Or, taxi.
Frk. Barners Kaelder Helgolandsgade 8A, Copenhagen 1653 Denmark We had very good food and service twice. Purposely returned as we enjoyed the first meal so much. Reservations ensured a table. Looking at current TripAdvisor reviews, some complain about service - it is popular; perhaps reviewers didn't reserve.
Restaurant Karla Dantes Plads 1, Copenhagen 1556 Denmark Food was good. Atmosphere was more "touristy" than the Frk. Barners Kaelder. Current reviews seem mixed - the place was very popular. Close to the National Museum so they may get a lot of walk-in traffic. We did a "walk-in" early in dining hours. Later, I think reservations would be required. Preferred the above over-all, but if you are near the National Museum, Karla is OK.
Adding - as noted above, Tivoli has a number of restaurants if you pay park admission. I have been disappointed with quality for price at the places I have tried, but others' experience may be more positive.