Up until now Autoptimize, when performing image optimization, relies on JS-based lazyloading (with the great lazysizes component) to differentiate between browser that support different image formats (AVIF, WebP and JPEG as fallback).
As JS-based Lazyload is going out of fashion though (with native lazyload being supported by more browsers and WordPress having out-of-the-box support for it too), it is time to start working on
For now that functionality is in a separate “power-up”, available on Github. If you have Image Optimization active in Autoptimize (and you are on the Beta version, Autoptimize 2.8.1 is missing a filter which the power-up needs so download & install the Beta if not done yet), you can download the plugin Github and give it a go. All feedback is welcome!