AVIF (and its image sequences) seems to be fairly complicated. Here's few comments [1] about it:
"Given all that I'm also beginning to understand why some folks want something simpler like webp2 :)"
"Despite authoring libavif (library, not the standard) and being a big fan of the AV1 codec, I do occasionally find HEIF/AVIF as a format to be a bit "it can do anything!", which is likely to lead to huge or fragmented/incomplete implementations."
Anyway, instead of adding FLIF, AVIF, BPG, and lots of similar image formats to web browsers, I think only one good format is enough and JPEG XR might be it. After something has been added to web browsers, it can't be removed.
Safari hasn't added support for WebP (which is good, there's no need for WebP after AVIF/JPEG XR is out) and it hasn't added support for HEIF (which is weird, considering Apple is using it on iOS), but maybe they know that there's no need to rush.
[1] https://bugs.chromium.org/p/chromium/issues/detail?id=960620...