It's very obviously built on the framework of Mario Odyssey (it's been developed by the same team, and there are a lot of common elements, particularly in the UI and visuals), but I would say it still has a distinct identity. DK's moveset and the whole concept of smashing up and throwing around the terrain are clearly a much better fit for DK than they would be for Mario.

It wouldn't surprise me at all if they started work on the game as a new Mario game with the central idea of destructible terrain, but then pivoted into DK when they realized that he's a better fit for the concept than Mario is (this is not uncommon for Nintendo; Kirby's Epic Yarn started as a new IP before they realized it fit pretty well as a Kirby game, among other examples), but either way I think it still stands out as not just being a Mario game.