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SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
It sounds like your best starting point would be to download or fork the repo https://github.com/mrdoob/three.js/, which contains the source of the website (not just threejs source). Then you can modify it bit by bit. You'll learn a lot by doing this, and you can move at your own pace, without being overwhelmed by too many technologies to learn.
you can find plenty of examples on gsap, react spring, lottie or polygonjs. But the choice would depend on what type of animation you want to achieve, how you want to create it, control it, etc