I actually decided to use avif on my project. But both this and webp is as fast as I know, not supported in any default image viewer on windows. Which is rater annoying, but I moved on to better programs for tgat anyways.
Avif is second to jxl though, some of the downsides of being a video format is that you loose progressive loading (only top to bottom iirc), degrades on re-encodes, and some other things I can't think of. Avif gets a win because if you have a av1 decoder you already have a avif decoder too! But since it is a video frame essential there are some downsides since some image specific features can't or won't be added.