Actually I did - when I made the post above, i was trying to remember why I hadn't done it and now I know - I remember jumping around and pressing all buttons, pulling triggers, in frustration - the only clear moves are jump, wall jump (which I thought was a double jump initially) and dash.
The issue is I didn't know you could "climb". Notice I worked it out right after the previous poster told me I could climb. You have little chance to find out you can climb by accident - because it only works when you happen to be in contact with the wall, which only lasts for a second, and even then, you have to be holding the trigger for it to happen, pressing everything experimentally won't work. So it requires foreknowledge.
After reading comments, I'm guessing most people here are Celeste fans. The only version I've played is the Pico8 one, the original. I guarantee you, if you test this game on non-Celeste fans, the majority of people will get stuck on the same point. I've had gamers get stuck on my games for far less egregious reasons than this during my testing sessions.