I rarely use oil or butter, unless I absolutely have to. I will only use oil if it is critical to the recipe or if I am a guest in someone's home. I do have the odd recipe where if you didn't use oil it just wouldn't cook properly. Like browning a crust, for example, might require a very small amount of oil brushed on.
As Amber mentioned, frying with a bit of water or veggie stock works fantastic, and happens to be my preferred method for sauteing. However, many of the veggies I used to fry, I now roast in the oven. I am so hooked on roasted veggies, I don't miss frying whatsoever. It really has opened the door to some amazing flavours. Like roasted cauliflower, broccoli, asparagus, and even spinach is delicious oven-roasted. It really is endless. I only had bad memories of okra from when my parent used to cook it. It's not really your average run of the mill vegetable, but I got brave and tried some roasted with a sprinkle of curry powder. Amazing!
There are those air fryers as well, which to me don't look like they hold enough to make them worth their while, but that's another option you could consider.