Ideas for mental games for my pup?

Looking for some fun games I can have my puppy work on. I read online that mind/stiffing games are important to not over excerise them but also make sure they aren’t bored. Preferably inside but outside too. I live in an area with pretty intense winters so I’d prefer inside.

For context, she’s a 15 week old American cocker spaniel puppy. She has a frozen Kong I’ll whip up on occasion. And only recently she was given a bully stick as an aid for her crate training. Any other good chewables? Someone told me beef kneecap?

Our apartment is moderately sized with a large partially fenced yard.

Thanks in advance!