WTF is it?

http://cubic-bezier.com/#.17,.67,.83,.67

Meat of this: a bunch of nice examples. Not just a rectangle bouncing back and forth.

https://callmenick.com/dev/level-up-animations-cubic-bezier/

https://easings.net/

GSAP

https://www.hongkiat.com/blog/css-cubic-bezier/