Can you give an example of what a typical high calorie / high carb day looked like for you?

I eat lots of carbs, always have... yet I don't seem to gain weight. I generally feel like, and am regarded by people who know me, as someone who "eats a ton" yet I have never struggled to lose weight.

The X food causes obesity theory is just too simple IMO, that or I have a tape worm or some kind of undiagnosed disorder that results in me maintaining a pretty consistent BMI despite eating whatever and whenever I want.

Have you ever tried tracking calories, not necessarily with the intention of hitting a goal? If not, the data can be rather informative, and doesn't necessarily match intuition. There's free apps like MyFitnessPal that makes it pretty easy. When I have done it, I've been able to correlate weight gain and loss to caloric intake. There are a few pounds of fluctuation from things like water retention and amount of food in your gut of course, but it's visible over the timespan of a week. If you eat a very consistent diet, you can measure differences on a scale across a few days.

I mean yes, that’s something of a tautology though.

Cutting down on calories necessarily means cutting down on fat, carbs, or both (technically protein as well, but protein doesn’t generally seem to be the issue.)

If you were to follow an explicitly low fat diet, it would be very difficult to eat junk food as well. Almost all junk foods are high in both fat and carbs at the same time.

You are right about refined carbs. Most public health organizations advise limiting one’s consumption of those.

I don't think "refined carbs are bad for you" is correct. Consider that many of the healthiest, least obese, longest lived societies on earth (e.g. Japan) have diets heavy in refined carbs (e.g. white rice).