The .avif image file should be able to be shared by Web Share. Adding avif to the other allowed image file types will help spread the use of it.
A website might like their users to be able to share their pictures and other files through social media, email, chat, etc. Since Web Share API is already shipped to more platforms like ChromeOS and Windows, but .avif is not supported yet. .avif showed better compression efficiency and better detail preservation than JPEG. In this regard, adding avif to web share will help spread the use of avif.
Explainers: https://github.com/w3c/web-share/blob/master/docs/explainer.md