Using animated GIFs as image layers

You can drag a .gif file inside of any top level banner, which will add it as a Figma image layer.

This method won't allow to include any other content over the top of the animated GIF, however, any additional Figma fills (eg color/gradient overlays) on this frame will also be included in the final .gif export.

Using animated GIFs as background fills on a frame layer

Alternatively, you can also drag a .gif file from your computer onto a frame layer's fill, which will set it as an image fill on the background of the frame. Any additional Figma fills (eg color/gradient overlays) on this frame will also be included in the final .gif export.

The advantage of this is that you can then add other Figma layers (text, images etc) inside of the frame on top of your animated GIF, and those will also be included in the .gif that gets exported with your HTML banners.