Just wanted to add that Celeste is one of the best games to get into speedrunning.
Unlike most games the dev actively worked with the speedrunning community and made the game as accessible as possible.
You're timed by the ingame clock and it pauses in between chapters so you can take a breather without affecting your time.
Here's what it looks like (My PB) I learned by doing 1 run a day and slowly improving (as well as watching other runners)