A simple scent game
Hide a few familiar treats in easy-to-reach places within one room and invite your dog to find them. Begin with obvious locations so the rule is clear. Avoid swallowable objects and account for treats in the normal diet.
Short play followed by rest
Try a familiar cue, a soft toy or finding a toy under a towel. Check the floor and avoid encouraging sharp jumps around furniture. A few relaxed minutes together can be more rewarding than a large collection of new toys.
Vary the kind of challenge
A scent game need not be followed by another difficult puzzle. Offer a familiar toy, a few calm movements on a rug, then rest. Notice what the dog enjoys: one searches patiently, another loses interest and prefers play with a person. Put the activity away before it becomes endless excitement. Indoor play should support the day, not require a dedicated room of equipment.
One game, three difficulty levels
Use a little food reward suitable for your dog and place it visibly beside the bed. Let them find it. Next, put it near the edge of a towel while keeping it visible. Only once the task is understood should you partly cover it with a loose corner.
The aim is relaxed searching, not an examination. If the dog chews the towel, becomes frustrated or leaves, simplify the task and remove the props. Supervise throughout; items small enough to swallow are unsuitable.
Finish before interest disappears. Note which version worked and begin there next time. Difficulty does not need to increase every day: a familiar successful task still provides something to do. Include food rewards in the daily allowance, then offer water and an opportunity to rest. The useful result is engaged, comfortable participation rather than the cleverest puzzle.
Useful? Save it for your next walk.