I'm not familiar with Adobe Animate. But I want to ask 2D artist to export animations from Adobe Animate to append to my HTML page. As for me the best way to append animations is SVG animations with CSS and avoid GIF because of its large size and raster-based. Are there possibilities to do that in Adobe Animate or could you recommend any external tool?
Not sure about "the best", since that's a very subjective judgement. However you can create HTML5 Canvas animations with Adobe Animate CC. It's mentioned on the Adobe Animate help website: Create and publish HTML5 Canvas documents in Animate.
Here's a brief quote from the page, just in case the link above rots.
Canvas is a new element in HTML5, which provides APIs that allow you to dynamically generate and render graphics, charts, images, and animation. The presence of the Canvas API for HTML5, strengthens the HTML5 platform by providing two-dimensional drawing capabilities. These capabilities are supported on most modern operating systems and browsers.
Essentially, Canvas is a bitmap rendering engine, and the drawings are final and cannot be resized. Furthermore, objects drawn on Canvas are not part of the web page's DOM.