[1] https://bugs.webkit.org/show_bug.cgi?id=207750#c25
And apple doesn't give ios uses any choice. You are stuck dealing with those differences.
Yeah, that's by far the worst part. Imagine being stuck with IE indefinitely. :)
https://www.coywolf.news/webmaster/why-webkit-supports-avif-...
https://libre-software.net/avif-test/
[1] https://bugs.webkit.org/show_bug.cgi?id=207750#c25