Not many processors have AV1 hardware decoders yet (Apple thru them in on their M3's last year and latest iPhone 15 Pros) so I can't see it being that. There's also software decoding that works fine. My wallpaper on macOS has been avif since last year (Sonoma) and works without issue. I don't think it works in Windows 10 tho. No issues with the latest Ubuntu and I'm not familiar at all with Android OS.
In any case, I think it's the best thing to come out in a long time. My website with raw PNGs was about 120MB. I crushed those PNGs with noticeable quality loss down to 50MB. I then crushed the original 120MB down to 60MB with minimal to no visual quality loss using webp. But I got it down to 25MB without loss using avif at 85% compression. Just insane performance, couldn't be more impressed!