Comment by SahAssar

Yes, by using the <picture> element with <source> elements declaring the individual formats with the last one being a regular <img> with the gif.

Or you could use content-negotiation to only send avif when it's supported, but IMO the HTML way with <picture> is perhaps clearer for the client and end user.

I think the webp problem was due to browsers supporting webp but not supporting animation, transparency or other features, so content negotiation based on mime types (either via <picture> or HTTP content-negotiation) did not work properly. Safari 16.1-16.3 has the same problem with AVIF, but that is a smaller problem than it was with webp.