in my app i was using jpeg but then switched to webp two years ago, they're for generating/displaying thumbnails for images and videos. and now avif seems like a better fit? anything that you're not happy about? considering avif now, appreciate any ideas

If you're working with images that need to be lossless or are simple in color diversity, WEBP is probably still a better choice (though not by a large margin). The biggest issue you might run into with AVIF is legacy support, particularly amongst Apple devices who were slower to implement support for it.

Otherwise the massive size reduction for storage and transfer speeds makes it incredibly attractive for modern web applications.