Author here: I'm also very much looking forward to using AVIF (and also JPEG XL), but it's another tooling question. I'm really hoping that Pixelmator Pro (now owned by Apple) will support them both soon. Photoshop (which I've recently dumped) supports WebP and AVIF, but not through the "Save for Web" or "Export As" flows. Having a nice export flow where you can easily compare compression vs. quality levels is really important to me, and I suspect to many others.