You can now convert avif files to jpg png and webp with this useful app.
An AVIF file is an image or pictured stored in the AV1 Image file format which was developed by the Alliance for Open Media. Its basically similar to a .JPEG or .PNG file. It is already supported by top popular media companies.
If you are looking for an image viewer that supports avif files then here you have it.

Avif is similar to heif image formats but its better with its better comression rate.