Edge browser now handles avif images.

bat999

Microsoft Edge browser v121 has now enabled avif images by default.
There's a test page...
here ---> https://libre-software.net/image/avif-test/

avif is well supported in web browsers.
There's a chart...

here ---> https://caniuse.com/avif

Good practice for websites is to offer a modern format, such as avif or webp.
Also with a jpeg fallback for legacy browsers.

MSE forum seems to be still using jpeg images.
But it's not the only culprit by any means.

Olinda99

why should they change to avif from jpg ?

booneruk

Olinda99 said:

why should they change to avif from jpg ?

They shouldn't, it could entail a massive piece of development work, especially implementing the fallback method that would be required to continue to support old browsers. 

However, if a site was being built from scratch and was very image heavy, then the reduced file sizes of the more modern file formats would mean performance would be improved for the end user. That's when it makes sense.