You might be mixing up containers and codecs. webm is the container format that most av1 video will be delivered in. With Apple the problem was not so much web

You might be mixing up containers and codecs. webm is the container format that most av1 video will be delivered in. With Apple the problem was not so much webm, but the vp9 codec, which is the codec most webm containers use (see youtube). ie, codecs: av1, vp9 <> h.264, h.265 containers: webm <> mp4