Apple is also on the list of organizations behind H.266 so it’s difficult to conclude anything beyond wanting to bet on all the horses.

that's not why Apply joined AV1. They joined AV1 because they were forced to. Netflix, Google, Amazon are all on the AV1 bandwagon. If Youtube, Netflix and Prime Video all use AV1 for future higher quality streams, Apple cannot avoid supporting it.

It works both ways: if popular devices don’t support it in decode, encoding your library in a format that is slow(er) to decode and/or more taxing on battery life isn’t a clear win.

Youtube has been vp9 only above 1080p for a long time, but Apple is adding support for VP9 only in the upcoming OS releases.