@mancerblack I'll give you a tip: download FreeTube. It's a free program that lets you watch YouTube for free without ads. The only problem is that you can't comment on videos with it, but that doesn't bother me. I make my comments on YouTube via the browser.
https://github.com/FreeTubeApp/FreeTube/releases This is the URL where you can download FreeTube. This solves the problem with the double sound on YouTube and the force that you have to deactivate the ad blocker on YouTube.

@leocg I use Opera One

In all other Chrome-based browsers, such as Chromium, Google Chrome, and Vivaldi, the Auto Dark Mode for Web Content works if enabled via the corresponding flags setting, except in Opera. Why is this? Personally, I find it a real shame because I have to use a dark mode extension in Opera, which never works properly anyway. Once activated, you don't need to configure anything in the menus of a dark mode extension, as every page is automatically darkened, even the pages where a dark mode extension fails.