@chaosxny Hello! I would like to add into this topic as I am also having the same issues.
This issue clearly was not present before as before the time of fontaine (August) all of the Event Pages and Version Preview Pages have been working in order.
Something must have had happened since Fontaine's Release (August onwards) or at least within this September that caused Hoyoverse's Event Websites' and Preview Websites' audio to act disabled. This had never been an issue in the past.
I have observed that this issue is present across Hoyoverse's Preview webpages, including ones released in the past, such as the following Version 3.1 Preview page (released September 2022):
https://act.hoyoverse.com/ys/event/e20220917prev/index.html?game_biz=hk4e_global&mhy_presentation_style=fullscreen&mhy_auth_required=true&mhy_landscape=true&utm_source=officialweb&utm_medium=news
And even with the most recent one released today, Honkai Star Rail's Version 1.4 Preview Page's audio, also is not working:
https://act.hoyoverse.com/sr/event/e20230929version-rpg/index.html?game_biz=hkrpg_global&mode=fullscreen&sign_type=2&auth_appid=rpg_version_page_140
Audio that does not work includes voicelines and background music that seems to be directly to the website itself. Embedded videos from Youtube (e.g., their Character Demo Video) works normally which is weird.
Something must have really been acting up in Opera GX that causes the audio in the website to be disabled.
I also concur with @rakewaza. I have also ensured that my Audio devices are in order; and it does not seem that audio devices are the problem since it does work with Google Chrome and Edge, without any hindrances.
I hope this post gains more attention as to resolve this issue immediately.