Yes, for animation a video codec like AV1 is much more suitable than a still image codec like JPEG XL.
JPEG XL does have some weak forms of inter prediction though (but they were designed mostly for still image purposes). One of them is patches: you can take any rectangle from a previously 'saved' frame (there are four 'slots' for that) and blit it at some arbitrary position in the current frame, using some blend mode of choice (just replace, add, alpha blend over, multiply, alpha blend under, etc). This is obviously not as powerful as full motion vectors etc, but it does bring some possibilities for something like a simple moving sprite animation. This coding tool is currently only used in the encoder for still images, namely to extract repeating text-like elements in an image (individual letters, icons etc) and store them in a separate invisible frame, encoded with non-DCT methods (which are more effective for that kind of thing) and then patch-add them to the VarDCT image. The current jxl encoder is not even trying to be good at animation because this is not quite its purpose (it can do it, but 'reluctantly').
Anyway, I think that animation is in any case best done with video codecs (this is what video codecs are made for), and I wish browsers would just start accepting in an <img> tag all the video codecs they accept in a <video> tag (just played looping, muted, autoplay), so we can for once and for all get rid of GIF.
I don't think this should be solved with tags (or other OOB methods). Just set a "loop" flag in the container (or metadata). GIF is perfect because it doesn't require ANY additional info when it comes to looping or animation.
Any format that doesn't have this is doomed to fail as a GIF replacement.
JPEG XL does have some weak forms of inter prediction though (but they were designed mostly for still image purposes). One of them is patches: you can take any rectangle from a previously 'saved' frame (there are four 'slots' for that) and blit it at some arbitrary position in the current frame, using some blend mode of choice (just replace, add, alpha blend over, multiply, alpha blend under, etc). This is obviously not as powerful as full motion vectors etc, but it does bring some possibilities for something like a simple moving sprite animation. This coding tool is currently only used in the encoder for still images, namely to extract repeating text-like elements in an image (individual letters, icons etc) and store them in a separate invisible frame, encoded with non-DCT methods (which are more effective for that kind of thing) and then patch-add them to the VarDCT image. The current jxl encoder is not even trying to be good at animation because this is not quite its purpose (it can do it, but 'reluctantly').
Anyway, I think that animation is in any case best done with video codecs (this is what video codecs are made for), and I wish browsers would just start accepting in an <img> tag all the video codecs they accept in a <video> tag (just played looping, muted, autoplay), so we can for once and for all get rid of GIF.