Moving thins from a downstream bug report: https://gitlab.gnome.org/GNOME/epiphany/-/issues/1639 I've epiphany-41.0-1.fc35.x86_64 and webkit2gtk3-2.34.1-2.fc35.x86_64. I do not know better pages, thus at least these. When I open https://finance.yahoo.com , then the lock icon menu in the address bar has "Deny" for everything, including Media Autoplay. However, when I Ctrl+click on an article link, which contains a video, then the video is started automatically. I see in the lock icon menu that the media autoplay is still disabled. When I open the link by writing the URL into the address bar, then the autoplay is not started, as expected. I thought the open in a new tab has its impact on this, but then I realized a simple non-Ctrl Click also ignores the media autoplay deny.
From what I can see, a video will autoplay if it was already loaded in a previous page. For instance, this website is good to test this: https://videojs.github.io/autoplay-tests/ On this video (https://videojs.github.io/autoplay-tests/plain/attr/autoplay.html), for instance, the first time it will not play automatically, but realoading the page (might) autoplay it.