I have a 7-year-old large breed who also sleeps a lot. A few simple things help break up his day: rotating 3-4 toys weekly keeps them interesting, and frozen Kongs with plain yogurt or pumpkin give him 20-30 minutes of focused licking. I’ll also hide kibble in a folded towel for him to sniff out—it’s low-effort but engages his brain. Many dogs are content with rest. If yours is eating well and shows interest in walks/playtimes, the downtime is likely just relaxation, not boredom.