The latest 1.22 contains among of bugfixes and Gstreamer VAAPI continues to have a good mainteince https://gitlab.freedesktop.org/gstreamer/gstreamer/-/commits/1.22?ref_type=heads in the main branch contains more commits about fixing problems, GStreamer VAAPI look's to be a good future.
Are you talking about the GStreamer un-maintained "vaapi" plugin or the new and maintained "va" plugin?
No response. I think the reporter was confused. Feel free to reopen if that's not the case. Also, questions should be sent to our mailing list webkit-gtk@lists.webkit.org and not to this bug tracker :)