UPDATE June 22
The Files & Photos app on iOS 16 supports AVIF images. The information page indicates that AVIF is supported. However, when the image is imported into the photos library, the format is changed to HEIF. While trying to open an image in Safari, it does not display and instead asks to be downloaded.
WebKit already supports AVIF. However, Safari relies on the underlying operating system for decoding and therefore had to wait for iOS to support AVIF. Safari will likely add support for AVIF within the subsequent two releases, now that iOS is no longer blocking AVIF.
AVIF
Alliance for Open Media has developed the AVIF image format, a format that makes images have a smaller file size than with JPEG, PNG, GIF, or HEIF, without sacrificing image quality. AVIF offers lossy and lossless compression and has already 70% support by web browsers. It is regarded as a significant advancement in media compression. It is the goal of AOMedia to create open, royalty-free software standards for multimedia distribution. Specifically, AVIF will be free for everyone to use. There is a long list of big companies behind AOMedia, including Netflix, Google, Facebook, Apple, and Microsoft. In terms of image file formats for the web, JPG and PNG are considered the most popular. Several years ago, Google developed a format called WebP that delivers images 30% smaller than JPGs, while maintaining image quality. With AVIF, images are 50% smaller than JPG while maintaining the same quality.
iOS
The iOS mobile operating system is Apple's mobile operating system that runs exclusively on iPhones, iPads, and iPod Touch devices. It is the second most widely installed mobile operating system in the world after Android. iOS was first released in 2007, along with the first iPhone. 2010 saw the development of an iPad OS version for tablets. Apple has since replaced this with iPadOS, a more open and modified version of iOS. Apple's apps, devices, and services are all part of the Apple Ecosystem, a collection of apps, devices, and services. The OS is designed to work seamlessly with other Apple platforms such as macOS, WatchOS, and Apple TV.
iOS AVIF support
Apple prefers to use HEIC (High-Efficiency Image File Format) as its default image format instead of AVIF for iOS. There is no imminent plan for Apple to support AVIF images locally on their devices. One of the mobile browsers still unable to display AVIF images is Safari. AVIF images can be viewed by iOS users using third-party web browsers such as Chrome or Opera Mobile. The problem is that users can't view AVIF images downloaded from the Internet on their Apple iOS devices, since the device itself doesn't support AVIF decoding. As soon as Apple decides to support the format, we can expect a massive switch to give support to Apple's ecosystem. Support for their browser Safari depends on OS support, as we explained in our Safari article.