Yes. Cosmetics only hide elements so they will never be able to do what you want.
So you need to use some Javascript-injection that can really change the behavior of things in a webpage, maybe a youtube extension can do it or Tampermonkey with a userscript. Because the problem will always be the autoplay, maybe an extension or userscript can stop it and then use cosmetics to hide it, but cosmetics alone are not for blocking.
I mean just installing https://chrome.google.com/webstore/detail/enhancer-for-youtube/ponfpcnoihfmfllpaingbgckeeldkhle seems to stop that behavior by default with no way to make channel trailers autoplay (which I won’t complain about). But that extension is really good, I used to use it in the past a lot, it even has a way to inject scripts in youtube and all now.
This one https://chrome.google.com/webstore/detail/improve-youtube-video-you/bnomihfieiccainjcjblhegjgglakjdd has nice features too, with the option to stop the channel trailer autoplay without affecting the player’s autoplay
Similar but different, but it shows there are many extensions available just to do that. I didn’t see any userscript for this though. so it seems only extensions are useful.