Netflix have switched to using AVIF and provided a good analysis and overview of competing formats in a recent blog post @ https://netflixtechblog.com/avif-for-next-generation-image-coding-b1d75675fe4

I don't think Netflix have switched, but they are prepping for doing so when they can and pushing companies to implement AVIF. Chrome seem to be very big on AVIF as it is essentially a successor to WebP (as AV1 is a successor to their VP video codec, and AVIF is a still version of AV1). Mozilla and many other Internet companies have joined "The Alliance For Open Media", who develop AV1 and AVIF.
It's very promising. The guy who founded MPEG even has a blog post essentially saying MPEG is dead, and "The Alliance For Open Media" has won. Competing open formats such as Xiph.org have also been folded into the efforts.
I hate all the politics (looking at Netflix's blog post you can see even JPEG 2000 is very similar in performance to AVIF - as these competing post-JPEG/MPEG formats are technically similar - it's ego and market domination and patents that is the true story here), but it's very pleasing to see that finally everyone has come together and got behind a royalty free organisation.

I thought I'd previously read something about Netflix using AV1/AVIF files on their iOS app and I should have said partly switched if true. AV1 support has been in the major browsers for a while now so it sounded plausible that Netflix may already be using it for video and images on target devices. JPEG 2000/XL was a worthy contender but AVIF does appear to be the future format and the winner of this race given the Alliance. Betamax vs VHS, the fight continues ;)

https://netflixtechblog.com/netflix-now-streaming-av1-on-android-d5264a515202

WebP was added to Safari 14, last year.

Re-summary as of today...

WebP is usable as soon as we drop IE11.

AVIF looks like it might be supported, if Safari adopts, and someone has made a patch for that.

JPEG XL seems likely to receive widespread adoption, based on recent discussions. They explicitly reference building on the shoulders of some of the other formats here, and it supports both lossy and lossless encoding. They also are trying to do everything, including supporting animation.

Probably the best strategy is to leapfrom WebP and AVIF, going straight to JPEG XL once that is supported across all our supported browsers. i.e. dump PNG and APNG (and gif) in favour of JPEG XL. A few years from now.

Recent article: https://cloudinary.com/blog/time_for_next_gen_codecs_to_dethrone_jpeg?utm_source=reddit&utm_medium=social&utm_campaign=time-for-next-gen-codecs-to-dethrone-jpeg

EDIT: We also need to consider PHP supporting JPEG XL too, which may take some time.