Hi, I released a program which replicates a feature made only in GameMaker Studio 2.3.
This program is a simple but robust animation curve editing tool.
Allowing you to create and import animation straight into your GameMaker projects.
It includes thorough documentation,
And includes an example to help you get started using it right away!
Link to the program:
https://fakeflxp.itch.io/animcurve
And I've also made a video explaining all the ways to use the program: