XnView Software

Currently, XnViewMP v1.3.1 does not handle AVIF images if the file extension is renamed to .HEIC or .HEIF.

As long as the container is HEIF, XnViewMP should handle common file extensions used for images in this container. For both AV1 and HEVC.

Windows supports this "natively", as long as you have the HEIF Image Extensions and AV1 Video Extension installed, both in thumbnails in Windows Explorer, but also when opening the files with the Microsoft Photos app.

I want to expand this suggestion and that XnView MP can be able to detect proper file format not only by file extension but by MIME type or what method is used in nconvert that allows to convert files with wrong extensions without error so when I open any file and XnView MP can't open/view it and raises error better do real format check 1st and try to auto-open/view file again. In GIMP there are no such problem and it opens file not matter what extension is (for example I can rename any supported media file to "1.dedbombom" and it would open it without any problems).
P.S. Sometimes it's working fine if webp renamed to png for example but if jxl rename to jpg then it's not opening.

+1 for both o-l-a-v and dedbombom