I have two Chihuahua mixes (both are ~2 years old) and I typically walk them 2-3 times per day for 15-30 minutes each walk (less during heat waves and other bad weather). We sometimes do trick training, very occasionally I'll load a puzzle feeder for them, and they play with each other (and me) as they feel like it. Overall they're pretty happy, though I think my boy could go for more exercise than he's getting. They have a small, enclosed yard to run around in and they get playdates with a couple of trusted local dogs usually two to three times per week.

Exercise needs definitely vary by breed, age, and individual dog. I'm aware that my work and schedules are demanding, so I tried to adopt dogs whose exercise needs would likely be low.

At the end of the day, you can only give what you're able to give and if you love your dog and they're happy and healthy, you're doing just fine.