@krasi1 Maybe first I will tell you how our plugin works. Our plugin converts images to WebP format and AVIF format, but does not change or delete the original images. It also doesn’t change image URLs.
When a browser tries to download an image file, the plugin checks if it supports the AVIF format (if enabled in the plugin settings). If so, the browser will receive an equivalent of the original image in the AVIF format. If it does not support AVIF, but supports the WebP format, the browser will receive the equivalent of the original image in WebP format. In case the browser does not support either WebP or AVIF, the original image is loaded. This means full support for all browsers.
The HEIC format is not supported by browsers other than Safari (https://caniuse.com/heif). This means that the original HEIC image cannot be used as an alternative to WebP and AVIF files.