@leocg
There is (obviously) a lot of confusion on this topic.
Understandably so, in my opinion - after a quick google search while I was trying to find the answer to this question, I found that all of the results on the first page had the same now-outdated information.
My Opera browser kept crashing, I ended up having to reinstall it, and had no idea I didn't need the special extension to add chrome extensions anymore because I never saw a notice, update, etc about it. It was just gone from the Opera Ad On website without explanation. It was the first extension I installed after downloading Opera and I never noticed it disappear.
I know you may not have control over making this kind of change but it would be really helpful if this information was updated on the Opera Help pages- it still says you need to install 'install chrome extensions' on Opera Add On website and provides the link to it that now brings you to 'the page you are looking for could not be found' message (perhaps other 'how-to' websites/blogs will start to update their pages).
If the link https://addons.opera.com/fr/extensions/details/install-chrome-extensions/ gave this update instead of just saying 'the page you are looking for could not be found' people trying to install the extension that no longer exists would understand why.
Sorry for the lengthy post... I know its probably not in your control- could you forward this to whoever is? I love using Opera and appreciate all the help articles, but they're only useful when kept up to date...