The movement in the gif guarantees a key cycle that allows you to gain height while the key door finishes opening,
making this dust bunny cycle possible. The inputs after the first room are:

1. buffer downleft dash while fastfalling,
2. buffer updash and drift into the right corner,
3. buffer upleft dash while fastfalling,
4. buffer downleftdash into corner,
5. buffer extended hyper, holding jump into keydoor.

If done correctly, you should be able to hold jump and clear the first column of dust bunnies.

Once madeline is on top of the first column of dust bunnies like so, right dash + demo + unbuffered right dash to have a clean landing.
Note: This is just my personal way of doing this key cycle; other top players probably have their own way of doing this so ask around for alternatives.