Repairable Bike Tips

I'm looking to purchase a bike (probably second hand) and I want to make sure that it'll be easily repairable in the future for at least standard maintenance stuff.

Thing is, I don't know anything about bikes- I've heard people say off hand that modern bikes might perform better but are less maintanable, is this a thing? What qualities/features in a bike tell me that it'll be easier to maintain in the long run?