Using Windows 10 here, so the OS could indeed be the reason. Although, I doubt this is the case. This issue with Opera is know for years, and none of the other browsers actually has an issue with playing videos. In that sense, it is truly a limitation of Opera...

Mmm, interesting. As for me when it is not YouTube 99% does not work. So are you saying that videos on let's say Facebook, just to pick one site, play for you? (an error occured while playing this video).

If yes, I am wondering what is different in/with your Opera installation. Also how it is different from the many others complaining about the same thing.

You mean 99.9% of the videos on YouTube? I am talking about other websites, where 0.1% of videos work. Unless it is embedded YouTube, but that is practically YouTube.

These are typical messages:

• The media could not be loaded, either because the server or network failed or because the format is not supported.

• html5: Video not properly encoded

It is long known that Opera does not play most videos out there on the web, something I have long accepted and just an alternative browser for these sources. However now with each new version update it pops-up with this Lucid mode marketing, which drives me crazy.
Please spend time on solving the ability to play videos in the first place, then only after (and very much after) spend time on improving what it plays. Useless.