I’d say 2021 is still pretty damn recent, most of my computing devices are still pre 2020. It’s also not just Apple, for example the latest Fairphone 6 doesn’t support it either. Images can still be pretty damn big when taken from a high resolution camera, and software decoding defeats the benefit from a format that’s supposed to be efficient. I’d say that it will probably take another decade for avif to become mainstream.

AV1 is only supported by new devices, most support VP9. For example, the iPad Air 2024 does not support AV1.