Imgur now blocks several VPNs and have issues loading embedded previews in several fediverse platforms. So instead of using imgur, you could use one of the following alternatives for uploading your images.
https://postimages.org/
https://imgbox.com/
https://imgbb.com/
https://www.imagebam.com/
Last one I promise
You need to use the direct links to the file ending with the file extension (.webp or .gif). Otherwise, you are asking it to embed a whole webpage, which is not possible. You can find the direct link by right clicking on the image and pressing copy image link.
Here are the proper embeds, if these don’t work, then jerboa doesn’t support embedding animated images.
gif 1
gif 2
gif 3