The two biggest games I can think of are 2D Mario and Switch Sports. Nintendo has gradually made the Switch more of a mass-market console over the last couple of years. The hardware got cheaper with the Lite, then we got Fitness Boxing, later Ring Fit, Brain Training, and soon Clubhouse games. Clubhouse games even has bowling from Wii Sports (or at least something similar) included! A new 2D Mario and Switch Sports would make perfect sense for the platform and elevate the Switch to even higher sales.
Other than that, sequels are a great way to keep interest in a platform up in the second half of its lifecycle. Breath of the Wild 2, the next Pokémon, Mario Kart 9 (although I don't think we'll see that this year already), the next 3D Mario and more are all possibilities.
