I noticed that Google PageInsights are including the AVIF video format in their Next Gen Format advice. I.e. If you are only using jpg or png images, you get this advice.
Apple have anounced support in Safari in next OS:
However, the need to provide a backup fallback video for all of the browsers that can’t display AVIF, still applies, and Google should really add that caveat in their advice.
SOURCE users - be sure to provide a Fallback Image using the Image Plus stack fallback settings, if using webP or AVIF formats.