AVIF is a new image format derived from the keyframes of AV1 video. It's a royalty-free format, and it's already supported in Chrome 85 on desktop. Android support will be added soon, Firefox is working on an implementation, and although it took Safari 10 years to add WebP support, I don't think we'll see the same delay here, as Apple are a member of the group that created AV1.

I'm not sure if that page is up to date. Firefox for Android and Chrome for Android both seem to support AVIF according to my tests. I'm not sure what "Android browser" means here, but it's been a while since I've seen the built-in browser engines not running on some recent version of Chromium as a base.

I don't expect Apple to ever implement AVIF. They have bought into HEIF as the new version of JPEG through licenses and hardware decoding and they're not exactly known of implementing open standards next to their own.

Encoding WEBP and AVIF and using the <picture> element on web pages should solve the bandwidth problem without depending on outdated browsers or lacking browser manufacturers. AVIF is better than WEBP in many cases, but WEBP is also better than JPEG or PNG in many places the older formats are still used.