Input combos? I'd definitely call things like extended hypers and wallbounces input combos, but for the basic air dash, I guess I don't consider pressing 2 buttons at the same time (dash + direction) to be worthy of calling a "combo". By that standard, jumping left/right or climbing up/down are also input combos.
On the other hand, though, I've seen friends of mine who are less experienced with video game controls struggle with all of the above actions. I could watch my friend manipulate the controller and see that she was only able to handle one button input at a time, so for example in order to jump right, she had to break it down into the discrete actions of: hold down the right button, hold down the jump button, release the jump button, release the right button, with maybe half a second to a full second in between each action. So for this friend, pressing any two buttons at the same time clearly was an "input combo" that was a challenge to execute.
The interesting thing to me is that in my mind, the basic controls of Celeste feel very simple: it's "only" run, jump climb, dash (until 7B and 8C teach you wallbounces and hypers). But all of those basic actions have so many subtleties. For example, jumps can also be wall jumps, and there are even two kinds of wall jumps: straight up the wall if you hold climb, which consumes climbing stamina, or away from the wall if you don't hold climb, which doesn't consume stamina (not counting the other wall jump type, neutral wall jumps, since those aren't taught or required to complete the game). Somehow all of this complexity felt very intuitive to me, even at the beginning when I still hadn't learned to execute it all consistently. So I never felt during my first playthrough that Celeste was somehow catering to speedrunners at the expense of the casual experience. In fact, my impression was that Celeste does a very good job of providing the smoothest possible ramp up from casual play to speedrunning.
Anyway, if there's a point to this meandering comment, it's that variation in the way that people perceive the complexity of video game controls is very interesting. The same friend I mentioned above, who had trouble stringing together two inputs in Celeste, can give me a run for my money in Mario Kart, managing steering, mini turbos, and using items all at once.