New WebKit Features in Safari 14.1
webkit.org>WebM Support
WebKit added improved support for WebM media. With Safari 14, WebKit added support for WebM via MSE on iPadOS and macOS. Now, WebKit on macOS supports WebM files containing VP8 or VP9 video tracks and Vorbis audio tracks. Developers can now offer WebM content to users, though users will enjoy the best quality and power efficiency with h.264 or HEVC.
No iOS, and the mention of power efficiency at the end I assume that means VP9 will be software decoded?
Edit: Still no VP9 showing up on Youtube. Although I am OK with 1080P AVC encode.
VP9 has hardware decode support on newer Macs.