I 100%'d Celeste and Celeste classic, and I can say this game is ridiculously difficult.
Pretty great, I mean it would be far worse if it was too easy, but sometimes the difficulty spikes that high, that you would spend like 5 minutes on the same fucking checkpoint.
They may or may not have cut a couple levels that would reduce the difficulty spike, which means you dive right into fcking action. In literally the first room of the second area you have to throw a snowball on spikes and then jump on it while it's rolling to progress further
Sometimes it feels like Item Abuse 3 level bullshit with the item juggling and everything, but then you do it and it feels incredible.
In general I think the game is rather fair and totally doable by a human. Really pushes the limits of what's possible in platformers