@leocg omg, I can't believe it's doable, what an easter egg! Yes, I can, however this still doesn't solve the problem, because I'm still not able to add a certain page/bookmark to many folders straight from here https://share.getcloudapp.com/YEudXEZr
The point of my request is to be able to add one bookmark to several folders from here https://share.getcloudapp.com/YEudXEZr
Why is this feature so important?
Imagine you have wide range of interests or you're a researcher and basically you catalogue things which you find and you need to do it in a certain way – i.e. history articles might cover many topics – WWII, land & naval battles and so on.
With the current solution (when you're not able to add bookmarks directly from the overflow element I posted above and you're able to manage it in truly inconvenient way by copying and pasting them like you showed me) I'm doomed to torment
Basically it'd be very convenient and probably might improve work of many people who've decided to use Opera.