I was the one who deleted it. Your exact comment was:
The core approach is firing an animation using either the intersection observer API or simply the scroll position of the page. A good article on how to do scroll animations with GSAP, the most common web animation library can be found here.
Since GSAP offers paid packages, to me it is a company. One you work for. That means recommending it falls under self-promotion, and you should follow the rules regarding promotion:
The community tends to vote down overt self-promotion and flag it as spam. Post good, relevant answers, and if some (but not all) happen to be about your product or website, that’s okay. However, you must disclose your affiliation in your answers.
To be clear, I am not saying the library you are recommending does not do what the asker wanted. It's certainly a good fit. But one of very many options, so you weren't recommending 'some options', you were recommending a very specific one.
I'm fine with you adding the comment again, IF you follow the rules about self-promotion. I think your expertise is valuable and you can add real value to the site. Of course you can refer to GSAP and its solutions when appropriate. Just make sure you stay on the right side of the spam line.