Mental stimulation for a gsd puppy?

I have a gsd mix who is about 6 months old. We do lots of physical activity (long walks, empty dog parks, playdates with other dogs, etc). We also go on long sniffing excursions, use lick mats, food puzzles, kongs, and bones, but I’m wondering if yall have any ideas for mental stimulation that doesn’t involve food! I feel like the only ways I can keep her mentally stimulated is food-focused, which I worry isn’t the healthiest. Any help is appreciated!