I bought a simple ranch style home with no basement a few years ago.
I have not done anything except change air filters and grease the
garage door rollers.

Is there anything else I need to be mantaining /checking? Is there an
internet checklist for 3-5 year old homes?

I have actually been renting it out and claimed almost $12k in
depcreciation over the last three years? What exactly is depreciating
that amount , as the home still feels like 'new' to me?