If you want to limit yourself specifically to 3D entirely free roaming Mario games, then sure it's been 8 years
But then you would be ignoring Super Mario 3D World + Bowser's Fury, yes I get the SM3DW part is a port from Wii U but the Bowser's Fury part is all-new and it's a (relatively short) 3D free roaming Mario game
You would also be ignoring Super Mario Bros. Wonder which was quietly one of the real GOTY releases in 2023 instead of whatever shit won
So saying Nintendo hasn't done anything with Mario for 8 years is kinda silly. They just haven't made a game exactly like Odyssey again, and considering how many decades it was between SM64 and Odyssey, you might be waiting a long long time if that's the only thing you specifically want