As the title says.
The .avif file is a file format similar to .heif/heic, but using the compression algorithm av1, which is an open source and free algorithm.
Details about .avif and av1 can be found in the following links:
Discourse doesn’t natively support it, so it’d be hard to add this feature. I think most pictures people want to upload would be JPGs and PNGs anyway, haha
Got it, haha. I believe that at some point in the future it will support .avif, which is indeed a very good format. 