The Nintendo DSi introduced dual cameras, but only a handful of games integrated them meaningfully. Here are the notable titles that used the camera:
The DSi cameras are low-resolution (0.3 megapixels / VGA) and lack autofocus. Most DSi titles do not use the camera at all. For more robust camera-based gameplay, consider Nintendo 3DS (AR Cards, Face Raiders) or Nintendo Switch (Labo, Ring Fit Adventure, Snap).